The 1909 LSU Tigers football team represented the LSU Tigers of Louisiana State University during the 1909 college football season. The LSU team posted a 6–2 record, losing to Southern Intercollegiate Athletic Association (SIAA) champion Sewanee and to an undefeated Arkansas. Notable victories include those over Mississippi and Alabama. John W. Mayhew, a former halfback at Brown, took over as coach for former Vanderbilt lineman Joe Pritchard midway through the season. College Football Hall of Fame inductee Doc Fenton started at quarterback.