三岛由纪夫（日语：三岛 由纪夫；假名：みしま ゆきお；平文式罗马字：Mishima Yukio，1925年1月14日－1970年11月25日），本名平冈公威（ひらおか きみたけ），日本小说家、剧作家、记者、电影制作人、电影演员与日本民族主义者。

三岛由纪夫是日本战后文学的大师之一，在日本文坛拥有高度声誉。三岛由纪夫诸多作品中，以1956年出版的《金阁寺》最为人所熟知，这是部充满悲剧性幻灭美学的作品，奥野健男当时曾赞赏该小说：「这是三岛文学的最高水平，三岛美学的集大成，本年度文坛的最大丰收。」除了日本国内，三岛的作品在西方世界也有崇高的评价，甚至有人誉称他为「日本的海明威」，曾三度入围诺贝尔文学奖提名，也是著作被翻译成英文等外国语版最多的当代作家。三岛性好热闹，三教九流之辈无不结交，好美酒，嗜佳肴，高朋满座，列位无虚席，十足是一位花花公子。高兴的时候，在别人家中还会表演倒立。但是，他在1970年时极端激进的政治目的自杀谏世事件，却使他在身后获得褒贬不一的个人评价。

Yukio Mishima (三島 由紀夫,Mishima Yukio) is the pen name of Kimitake Hiraoka(平岡 公威,Hiraoka Kimitake, January 14, 1925 –November 25, 1970), a Japanese author, poet, playwright, actor, and film director. Mishima is considered one of the most important Japanese authors of the 20th century. He was considered for the Nobel Prize in Literature in 1968 but the award went to his fellow countryman Yasunari Kawabata. His works include the novels Confessions of a Mask and The Temple of the Golden Pavilion, and the autobiographical essay Sun and Steel. His avant-garde work displayed a blending of modern and traditional aesthetics that broke cultural boundaries, with a focus on sexuality, death, and political change. Mishima was active as a nationalist and founded his own right-wing militia. He is remembered for his ritual suicide by seppuku after a failed coup d'état attempt, known as the "Mishima Incident".