Nihon-shiki or Nippon-shiki (日本式 "Japan-style"; romanized as Nihon-siki or Nippon-siki in Nippon-shiki itself) is a romanization system for transcribing the Japanese language into the Roman alphabet. It is said to conform more closely to the kana writing system but, as it does not follow familiar patterns of English spelling, native speakers of English find its spelling counterintuitive.

The system was invented by physicist Aikitsu Tanakadate (田中舘愛橘) in 1885 and is the direct forbear of the more popular Kunrei-shiki romanization system.

Note:

• Those in red are outdated in the language itself.
• When he へ is used as a particle it is written he not e (Kunrei-shiki/Hepburn).
• When ha は is used as a particle it is written ha not wa.
• When wo を is used as a particle it is written wo not o.
• Long vowels are indicated by a macron, for example long o is written ō.
• Syllabic n ん is written as n before consonants but as n' before vowels and y.
• Geminate consonants are marked by doubling the consonant following the っ, without exception.

The difference between Nippon-shiki and Kunrei-shiki is the differences between the kana syllabary and modern pronunciation. In modern standard Japanese, the sounds of the pairs di/zi ぢ/じ, du/zu づ/ず, dya/zya ぢゃ/じゃ, dyu/zyu ぢゅ/じゅ, dyo/zyo ぢょ/じょ, wi/i ゐ/い, we/e ゑ/え, kwa/ka くゎ/か, gwa/ga ぐゎ/が have become identical. For example, the word kanadukai (Nippon-shiki) かなづかい is pronounced as kanazukai in the modern Japanese.

Nippon-shiki sometimes said to be more regular, as it maintains a strict one kana, two letters form. Because it has different forms for the pairs listed above, it is the only system of romanization that allows lossless mapping to and from kana (see the hiragana article for more details).

Nippon-shiki has been recognized as ISO 3602 strict form. The JSL system, which is targeted at foreign students of Japanese, is also based on Nippon-shiki.