Tadashi (Kanji: 正, 禎, 忠, 荘, 匡史 Hiragana: ただし), Japanese masculine name, may refer to :

• Tadashi Abe (阿部 正, 1926-1984), the first aikido master to live and teach in the west
• Tadashi Agi (亜樹 直, 1962-), Japanese manga story writer, novelist and screenwriter
• Tadashi Hayashi (林 正, born 1962), Japanese basketball coach
• Tadashi Honda (本多 忠, born 1951), Japanese swimmer
• Tadashi Inuzuka (犬塚 直史, 1954-), Japanese politician
• Tadashi Iijima (飯島 正, 1902–1996), Japanese film critic
• Tadashi Irie (入江 禎, 1944-), a Japanese yakuza boss
• Tadashi Ishimine (伊志嶺 忠, 1985-), baseball catcher for the Tohoku Rakuten Golden Eagles
• Tadashi Kato (加藤 忠, born 1935), Japanese cyclist
• Tadashi Kashiwada (柏田忠, 1964-),artist,painter
• Tadashi Kawamata (川俣 正, 1953-), a Japanese plasticist
• Tadashi Kuranari (倉成 正, 1918-1996), Japanese politician
• Tadashi Lometo, Marshallese politician
• Tadashi Mihara (三原 正, born 1955), Japanese boxer
• Tadashi Miyazawa (宮澤 正, born 1955), a Japanese voice actor
• Tadashi Mori (森 正, 1921-1987), Japanese conductor and flautist
• Tadashi Munakata (宗像 政, 1854–1918), Japanese politician
• Tadashi Nakamura (disambiguation)
• Tadashi Obara (小原 唯志, born 1983), Japanese speed skater
• Tadashi Ohtsuka (大束 忠司, 1978-), Japanese badminton player
• Tadashi Okamoto (岡本 正, born 1947), Japanese boxer
• Tadashi Saito (斎藤 直, born 1938), Japanese rower
• Tadashi Sasaki (disambiguation)
• Tadashi Sato, American artist
• Tadashi Sawamura (沢村 忠, 1943–2021), Japanese kickboxer
• Tadashi Shimada (嶋田 忠, 1949-), Japanese photographer
• Tadashi Shimizu (清水 忠史), Japanese communist politician
• Tadashi Shimokawa (下川 禎, born 1962), Japanese fencer
• Tadashi Shoji, fashion designer
• Tadashi Suetsugi (末次 忠司, 1958–), a Japanese engineer
• Tadashi Suzuki (鈴木 忠志, born 1939), a theatrical director, writer
• Tadashi Takamura (高村 規, 1933-2014), Japanese photographer
• Tadashi Wakabayashi (若林 忠志, 1908–1965), Japanese/American baseball player
• Tadashi Watanabe (渡辺 貞, born 1944), Japanese computer engineer
• Tadashi Yamamoto (1936–2012), Japanese internationalist
• Tadashi Yamamoto (athlete) (山本 忠司, 1925–1998), Japanese triple jumper
• Tadashi Yamashita (山下 忠, born 1941), Japanese American martial artist
• Tadashi Yanada梁田 貞 (1883–1959), Japanese composer
• Tadashi Yanai (柳井 正, born 1949), Japanese billionaire and richest man in Japan
• Tadashi Yokouchi (横内 正, born 1941), Japanese actor

Fictional characters

• Tadashi Hamada, a character from Big Hero 6
• Tadashi Karino (狩野 宙), a character from anime series S.A: Special A
• Tadashi Yamaguchi (山口 忠), a character from Haikyuu with the position of middle blocker from Karasuno High