Doctor Sax (Doctor Sax: Faust Part Three) is a novel by Jack Kerouac published in 1959. Kerouac wrote it in 1952 while living with William S. Burroughs in Mexico City.

The novel was written quickly in the improvisatory style Kerouac called “spontaneous prose.” In a letter to Allen Ginsberg dated May 18, 1952, Kerouac wrote, “I’ll simply blow [improvise like a jazz musician] on the vision of the Shadow in my 13th and 14th years on Sarah Ave. Lowell, culminated by the myth itself as I dreamt it in Fall 1948 . . . angles of my hoop-rolling boyhood as seen from the shroud.” In a letter to Ginsberg dated November 8 of the same year, Kerouac admits “Doctor Sax was written high on tea [marijuana] without pausing to think, sometimes Bill [Burroughs] would come in the room and so the chapter ended there, . . .” (ibid, p. 185).