Abstract: An air grease gun includes a grip, a barrel, a spout pipe unit and a grease storage tube. A generally Y-shaped air passage is formed in the grip and is bifurcated into a first branch and a second branch at the lower end portion of the grip. A compressed air source is communicated with the first branch. The second branch is communicated with the lower air chamber of the grease storage tube via an air tube. A valve normally closes the upper section of the air passage, which is above the first and second branches. The compressed air flowing from the compressed air source enters the grease storage tube via the first and second branches and via the air tube so as to push a tube piston upward, thereby impelling the grease in the grease storage tube into the barrel. Upon actuation of a trigger, the valve opens the air passage so that the compressed air flows into the barrel through the upper section of the air passage, thereby pneumatically moving the grease in the barrel to the spout outlet of the gun.