The 1931 Cal Poly Mustangs football team represented California Polytechnic School—now known as California Polytechnic State University, San Luis Obispo—as a member of the Northern California Junior College Conference (NCJCC) during the 1931 junior college football season.
Led by tenth-year head coach Al Agosti, Cal Poly compiled an overall record of record of 3–5–1, with a mark of 3–2 in conference play, placing third in the NCJCC.
The Mustangs played home games in San Luis Obispo, California.
Cal Poly was a two-year school until 1941.
The Mustangs did not field a team in 1930 due to a polio epidemic.