Korean Cucumber Soup (Oi Naengguk) - Best Cold Summer Soup

Name: Korean Cucumber Soup (Oi Naengguk) Recipe
Prep time: 5 min
Cook time: 5 min
Total time: 10 min
Ingredients: 1/3 cucumber; 1/4 onion; 10 g rehydrated seaweed; 1 tbsp sugar; 0.5 tbsp maesil-cheong (Korean plum syrup); 1 tsp salt; 1/2 tsp minced garlic; 3 tbsp vinegar; 2 tbsp chamchi-aekjeot; 500 ml water; 1 cup ice; 1 tbsp sesame seeds; 1 red chili pepper (optional)

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Korean cucumber soup (오이냉국) is a Korean cold soup made with cucumber and seaweed in a sweet, tangy broth, served chilled. Total time: 5 minutes. Serves 4. When summer hits over 30°C and no one even wants to eat, this is the exact dish Korean moms make. My mom makes it every summer and it’s a dish that often shows up as a side dish at Korean restaurants too. So for me, it’s my ultimate summer soul food. This oi naengguk will be the cold cucumber soup that gets you through the heat.

Korean cucumber soup garnished with sliced red chili pepper — A light, clean bowl of cold cucumber soup to cool your body down.

Why My Mom Makes Oi Naengguk Every Summer 🥒

In Korea, summer is always above 35°C. Unlike European summers, it’s incredibly humid, you sweat and you really don’t even want to cook anything that involves turning on the stove. That’s when this cold cucumber soup naturally comes to mind. Ready in 5 minutes, no cooking, ice-cold, sweet and tangy so it quenches your thirst too. That kind of summer food!

Oi naengguk topped with ice cubes and toasted sesame seeds and red pepper — This Korean cucumber soup is the dish my mom makes every summer.

Korean Unnie Tip👱🏼‍♀️

My mom used to add somyeon (thin wheat noodles) to this. Then it becomes another delicious Korean cold noodle dish!

10 Best Korean Cold Noodles You Must Try This Summer

A Summer Dish for Staying Hydrated

Cucumbers are about 95% water, which makes them a really great ingredient for hydration in the summer. On top of that, this Korean cucumber soup is low in calories and the seaweed adds iodine, which supports thyroid function and skin health. I’d call it a wellness superfood.

Low-calorie Korean cucumber soup, a wellness dish my mom always trusted — Sweet, sour, a little salty, the balance that makes this cold cucumber soup so tasty!

Ingredients for This Cold Cucumber Soup

For Vegetables and other ingredients

1/3 cucumber
1/4 onion
10g rehydrated seaweed

For Broth

500ml water
1 cup ice
1 tbsp sugar
0.5 tbsp maesil-cheong (Korean plum syrup)
1 tsp salt
1/2 tsp minced garlic
3 tbsp vinegar
2 tbsp chamchi-aekjeot (tuna fish sauce) – can substitute with 1 tbsp guk-ganjang (Korean soup soy sauce) or 1 tbsp fish sauce

For Garnish

1 tbsp sesame seeds
1 red chili pepper (optional)

simple ingredients for the summer Korean cold soup with cucumber, oi naengguk — What you need for this best Oi Naengguk

Where to Buy Korean Ingredients Outside Korea

Maesil-cheong(plum syrup) and chamchi-aekjeot(tuna sauce) can be hard to find depending on where you live. If there’s a Korean grocery store near you (H Mart, or a local Korean market), you can find them there. Online, you can also get them on Amazon.

Tuna Kimchi Jjigae — Plum syrup on Amazon👆

If you really can’t find maesil-cheong, use half the amount of sugar that the maesil-cheong would call for, and add the same amount of lemon juice.

How to Make Korean Cucumber Soup

Step 1. Rehydrate the dried seaweed

Soak the dried seaweed in cold water for however long the package says. Squeeze out the excess water. If the pieces are big, cut them into bite-sized pieces with scissors.

Dried seaweed soaking in cold water for Korean cucumber soup — Soak the dried seaweed until it’s fully soft.

My mom, and honestly all Koreans, cut it with kitchen scissors because using a cutting board and knife is too much of a hassle haha. Or you can buy pre-cut dried seaweed like the one I used today.

pre cut dried seaweed — Cut dried seaweed 👆

kitchen aid kitchen shears — Cut dried seaweed 👆

Step 2. Prep the vegetables

Julienne the cucumber and onion into thin strips, and mince the garlic finely.

Step 3. Mix the broth

In a mixing bowl, add the water, sugar, salt, maesil-cheong(plum syrup), minced garlic, vinegar, and chamchi-aekjeot(tuna sauce), and mix well.

This is where you really need to taste it. My mom always told me the broth should taste a little saltier and a little more sour than you’d want it to be. That way, as the ice melts, the flavor mellows out and ends up perfectly seasoned. If it tastes right now, it’ll go bland and flavorless once the ice melts!

Julienned cucumber and thinly sliced onion on a cutting board for oi naengguk — Prepare vegetables for cold cucumber soup

Korean cucumber soup broth made by Korean tuna sauce and vinegar — Prepare vegetables for cold cucumber soup

Step 4. Combine everything

Add the julienned cucumber, onion, and rehydrated seaweed into the broth and stir gently so everything mixes together evenly.

Adding julienned cucumber and onion to the oi naengguk broth — Add the vegetables and seaweed into the broth

Step 5. Serve ice-cold

Add ice, sprinkle sesame seeds generously, and top with red chili pepper for some color. If you don’t like spicy, you can leave the chili pepper out.

Hydrating cold cucumber soup bowl with fresh cucumber and seaweed — Finish with sesame seeds and red chili pepper

Korean metal bowl — cold noodles bowls on Amazon 👆

Why My First Oi Naengguk Was a Disaster 🥺

I tasted the broth before adding ice and it was perfectly seasoned, then I added ice and it went bland. The broth needs to taste saltier and more sour than you’d want before the ice goes in, so once the ice melts, it ends up perfectly seasoned when you actually eat it.
Don’t get greedy with the seaweed. It expands a ton once rehydrated, and you can end up with something closer to miyeok-guk (seaweed soup) than Korean cucumber soup.

Substitutions & Variations I’ve Tried

Chamchi-aekjeot → guk-ganjang: This swap works, but chamchi-aekjeot gives this Korean cucumber soup a deeper umami than guk-ganjang does.
Chamchi-aekjeot → regular fish sauce: Chamchi-aekjeot(tuna sauce) has a stronger umami and doesn’t have that fishy smell.
Maesil-cheong → honey or sugar: These add sweetness, but they don’t replace the tartness and fruity aroma maesil-cheong gives, so the soup loses some depth of flavor.
Skip the seaweed: This is just my personal take, but cucumber and onion alone make this cold cucumber soup plenty delicious. Simpler and cleaner.

Close-up of cold cucumber soup broth with julienned cucumber and rehydrated seaweed — Hydrating cold cucumber soup bowl with fresh cucumber and seaweed.

How to Store and Serve

If you need to prep ahead: Make just the broth and keep it in the fridge (up to 2 days). When you’re ready to eat, julienne fresh cucumber, add ice, and bring it to the table, freshly made oi naengguk, done!

What I Serve Alongside Korean Cucumber Soup

Oi naengguk is more like a side dish.

Bibimbap: The cold, sweet-tangy cold cucumber soup balances out the warm, spicy bibimbap.

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Korean BBQ: It washes away the greasiness of the meat. You’ll often see oi naengguk served at Korean BBQ restaurants.

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Somyeon: My mom sometimes boils somyeon (thin wheat noodles) and adds it in here, it’s a summer special menu from my mom.

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Traditional oi naengguk with crunchy julienned cucumber and rehydrated seaweed — Korean cucumber soup showing up as banchan at a Korean BBQ restaurant, just like at home.

FAQ about Oi Naengguk

Oi naengguk is a side dish. In Korean meals, it comes to the table alongside rice and other side dishes. You’ll often see it served at Korean BBQ restaurants too.

You can make the broth ahead of time. Just add the cucumber and ice right before serving, that way it tastes freshly made. But honestly, if you’re eating it that same day, it’s totally fine to make it a few hours ahead too.

Yes, of course. You can substitute 1 tbsp of guk-ganjang. This turns it into a fully vegan version of this Korean cucumber soup.

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By Blonde Kimchi

Korean Cucumber Soup (Oi Naengguk) Recipe

This Korean cucumber soup is a Korean cold soup of cucumber and seaweed in a sweet-tangy broth. A no-cook 5-minute dish my mom makes every summer.

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Course: Side Dish, Soup

Cuisine: Korean

Keyword: bibim guksu, mom’s recipe, No-Cook, Non-Spicy, Seafood, Seaweed, summer, Under 10 Minutes

Mood: Refreshing

Difficulty: Easy

Prep Time:5

Cook Time:5

Total Time:10

Servings: 4 people

Calories: 49kcal

Equipment

Ingredients

1/3 cucumber
1/4 onion
10 g rehydrated seaweed

Broth

1 tbsp sugar
0.5 tbsp maesil-cheong Korean plum syrup
1 tsp salt
1/2 tsp minced garlic
3 tbsp vinegar
2 tbsp chamchi-aekjeot Korean tuna fish sauce: can be substituted with 1 tbsp guk-ganjang (Korean soup soy sauce) or 1 tbsp fish sauce
500 ml water
1 cup ice

Garnish

1 tbsp sesame seeds
1 red chili pepper optional

Instructions

Soak the seaweed in water ahead of time to rehydrate.
10 g rehydrated seaweed
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Thinly julienne the cucumber and onion, and mince the garlic.
1/3 cucumber, 1/4 onion, 1/2 tsp minced garlic
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In a mixing bowl, add sugar, salt, maesil-cheong, minced garlic, vinegar, and chamchi-aekjeot. Then pour in the water and stir to make the broth.
1 tbsp sugar, 0.5 tbsp maesil-cheong, 1 tsp salt, 3 tbsp vinegar, 2 tbsp chamchi-aekjeot, 500 ml water
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Add the cucumber, onion, and rehydrated seaweed to the broth and mix together.
1/3 cucumber, 1/4 onion, 10 g rehydrated seaweed
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Add ice, sprinkle sesame seeds, and place red chili pepper on top.
1 cup ice, 1 tbsp sesame seeds, 1 red chili pepper
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