Jackson police spokeswoman Officer Colendula Green says the incident occurred about 2:30 a.m. Tuesday at a Shell convenience store near downtown.
Green says police are looking for two masked gunmen but fled the scene without taking any money.
Green says the clerk was shot in the leg and is listed in stable condition at the University of Mississippi Medical Center.
She says the security guard, who died at the scene, was shot in the upper torso and left arm. Authorities have not released his name.