It happened around 7:30am at a game room on the East Freeway at Sjolander in Baytown.
According to deputies, three Latino males were inside gambling when they turned to rob the place. Shots were fired and the security guard was killed at the scene. His name has not been released.
The suspects fled in a dark-colored SUV. Deputies are not sure how much cash the suspects got away with, but there was a large amount on the ground outside.
Anyone with information can call the Harris County Sheriff's Office or Crime Stoppers.