Authorities said the suspects entered the market in the 1700 block of Lakewood Boulevard at about 9:25 p.m. Tuesday. The men went register to register, stealing about $250, before escaping.
The supermarket was open at the time, packed with customers.
One of the gunmen pistol-whipped the store manager. He was taken to the hospital with a head injury.
No customers were hurt, but they were detained as sheriff's deputies searched the store.
Anyone with information is urged to call the Lakewood Sheriff's Station at (562) 623-3500.