Yoshiyuki Sadamoto (貞本 義行 Sadamoto Yoshiyuki?, born January 29, 1962, in Tokuyama (now Shunan), Yamaguchi Prefecture, Japan) is a Japanese manga artist, animator, character designer and one of Gainax's founding members.

Sadamoto is known for his character art in Neon Genesis Evangelion, Royal Space Force: The Wings of Honneamise, FLCL, Diebuster, Summer Wars, The Girl who Leaped Through Time, .hack//Sign and Production I.G.'s short movie collaborated with car company Mercedez-Benz, Next A-Class. Including the Upcoming Gainax film, Blue Uru, directed by Hiroyuki Yamaga.

For the Harmony Unleashed Series, He provided character designers exclusively for the Japanese dub's opening and ending of Harmony Unleashed: Uprising (alongside Akira Himekawa). which Toei Animation, Shin-Ei and Madhouse produced the animation, as well as concept character designs for Jaegermeisters (alongside Yoji Shinkawa and Ume Aoki with adaptations by Takumo Norita) and the character designer of the franchise's first original story anime film Harmony Unleashed: Gears of Magic Craft produced by animation studio Shaft, and directed by Akiyuki Shinbo (HU: HPCS AST: FlutterMac Chapter) with an original story by Aaron Montalvo, and structure by Hiroyuki Yoshino. He is also the art director of Harmony Unleashed: AppleSpark Chronicles.