No. 20 Madras Mail is a 1990 Indian Malayalam-language comedy thriller film directed by Joshiy and written by Dennis Joseph from a story by Harikumar. The film stars Mohanlal in lead role and Jagadish, Maniyanpilla Raju, M. G. Soman, Ashokan, and Suchitra Murali in supporting roles, while Mammootty appears in an extended cameo as himself. The background score was composed by S. P. Venkatesh while the song was composed by Ouseppachan. The plot follows three youngsters who are embroiled in the murder mystery of a young woman in a train journey from Thiruvananthapuram to Madras.

No.20 Madras Mail was released on 16 February 1990 and received positive reviews. Almost half of the film was shot inside a train. Four years later, the film was remade in Hindi as Teesra Kaun by Partho Ghosh.