Sing a Song of Sex (日本春歌考, Nihon shunka-kō, literally: A Treatise on Japanese Bawdy Songs) is a 1967 Japanese New Wave musical film directed by Nagisa Ōshima. The Japanese title of the film derives from a book of the same name, a treatise on Japanese erotic songs written in 1966 by Tomomichi Soeda. Though there are four credited writers, much of the film was improvised by the actors. The story follows four high school seniors on their erotic daydreams and peripatetic outings across Tokyo after having taken their university entrance exams. They have one fateful night of drinking and singing with one of their teachers, who sings a bawdy song that becomes the main musical theme of the story.

The film, in avant-garde fashion, is more a collage of scenes than a coherent narrative. The director once said that the film is "about the imaginary." It is not pornographic and contains little nudity. It was screened at Harvard in 2008 as part of their "Nagisa Oshima and the Struggle for a Radical Cinema" program. The film appeared in Kinema Junpo's 1999 list of the 120 best Japanese films of all time as voted by film experts.