The 1991 Idaho Vandals football team represented the University of Idaho in the 1991 NCAA Division I-AA football season. The Vandals were led by third-year head coach John L. Smith, were members of the Big Sky Conference and played their home games at the Kibbie Dome, an indoor facility on campus in Moscow, Idaho.
The Vandals missed the I-AA playoffs for the first time since 1984. Led by sophomore quarterback Doug Nussmeier, Idaho finished the regular season at and in the Big Sky. The Vandals defeated rival Boise State for the tenth consecutive season.