331st

331st may refer to:


 * 331st Air Expeditionary Group, inactive United States Air Force unit
 * 331st Fighter-Interceptor Squadron, former unit of the United States Air Force
 * 331st Guards Airborne Regiment, formation of the Russian Airborne Troops, part of the 98th Guards Airborne Division
 * 330th Rifle Division (Soviet Union), former infantry division of the Red Army in summer 1941