31st Battalion may refer to:
31st Battalion, Royal Queensland Regiment, a unit of the Australian Army 31st/42nd Battalion, Royal Queensland Regiment, a unit of the Australian Army 2/31st Battalion (Australia), a unit of the Australian Army that was raised during World War II 31st (Alberta) Battalion, CEF, a unit of the Canadian Army 31st Infantry Battalion (Estonia), a unit of the Estonian Army 31st Engineer Battalion, a unit of the United States Army Combat Logistics Battalion 31, a unit of the United States Marine Corps
See also 31st Division (disambiguation) 31st Group (disambiguation) 31st Brigade (disambiguation) 31st Regiment (disambiguation) 31st Squadron (disambiguation)