Japanese Long Vowels: おう vs おお, ―, and When Vowels Get Extended

Japanese vowels can be short (one beat) or long (two beats). Getting long vowels right matters — saying a word with the wrong vowel length changes its meaning or makes it sound unnatural.

Long Vowels in Hiragana

In hiragana, long vowels are written by adding a second vowel character:

The Special Case: おう vs おお

The “oo” sound can be spelled two ways in hiragana, and this is one of the trickiest parts for learners:

• おう (ou): Most “o” long vowels are spelled this way, even though both characters together are pronounced as a single long “oo” — NOT as “o-u”
• おお (oo): A few words genuinely use おお, particularly おおきい (ookii, big), おおい (ooi, many), おおかみ (ookami, wolf)

The rule: you must memorize which words use おう and which use おお. However, they’re pronounced identically.

Long Vowels in Katakana

In katakana, ALL long vowels are written with the long vowel mark ー (chōonpu). This makes katakana simpler for long vowels than hiragana.

• コーヒー (koohii) — coffee [ko-o-hi-i]
• スーパー (suupaa) — supermarket
• ノート (nooto) — notebook
• ケーキ (keeki) — cake

Common Mistakes

• Shortening long vowels: こうえん (kouen, park) said as “ko-en” sounds unnatural — the “ou” should be held for two beats
• えい (ei) confusion: Many learners pronounce えいご as “e-i-go” (three syllables) instead of “ee-go” (two syllables)
• Miss-spelling おう vs おお: This is a spelling issue, not a pronunciation one — both sound the same

Words to Practice

• おかあさん (okaasan) — mother [o-ka-a-sa-n]
• おとうさん (otousan) — father [o-to-u-sa-n = o-too-san]
• せんせい (sensei) — teacher [se-n-se-i = sen-see]
• おおきい (ookii) — big [o-o-ki-i = oo-kee]
• こうえん (kouen) — park [ko-u-e-n = koo-en]

Yuka & Rei Get Long Vowels Right

Learning kana feels abstract until you see how real learners talk about it. Here is Yuka working through the tricky parts — and Rei making the explanations click. Their questions are probably the same ones you have.

Yuka

Rei, I wrote おばさん meaning grandmother and my friend laughed. I thought that was right?

Rei

The long vowel strikes again! おばさん (3 morae) = aunt or middle-aged woman. おばあさん (4 morae, long あ) = grandmother. One extra beat changes everything. This is why long vowels matter — they change meaning, not just pronunciation.

Yuka

How are long vowels written in hiragana?

Rei

In hiragana, long vowels are written by adding the vowel character: あ → ああ (long a), い → いい (long i), う → うう (long u). But お sounds are often extended with う: おとうさん (father) is read おとおさん. In katakana: always ー for any long vowel — コーヒー, スーパー.

5 Practice Examples — Read These Aloud

These examples use the characters from this article in real words. Say each one aloud and try to recall the article’s rules as you read.

1. おかあさん (okaasan) — mother (long あ)
2. おとうさん (otousan) — father (long お written with う)
3. おにいさん (oniisan) — older brother (long い)
4. コーヒー (koohii) — coffee (ー marks long vowel in katakana)
5. すうじ (suuji) — number/numeral (long う)

Your Turn! Write Your Own Example in the Comments

The fastest way to remember kana is to write words you already know in Japanese script. Try writing your name, your hometown, or your favourite food using the characters from this article.

Share what you wrote in the comments — other learners will see it, and writing for an audience makes the learning stick twice as fast. Log in to save your comment history and join the Top Commenters ranking!

Keep Learning: Kana Hub | Grammar | All Kana Articles | Start Learning Japanese