Abstract: A pneumatic greaser has a body and a barrel. A piston is movably received in the body and defined with a valve hole at a rear end thereof. A pole is formed on the pole plate positioned in the piston. Multiple linkages extend through the pole plate and are connected with an exterior sheet and an interior sheet. A valve spring is provided between the exterior sheet and the pole plate. A valve shaft extends through the valve hole. A rear cushion is mounted on a rear end of the valve shaft. A front cushion is mounted outside the exterior sheet. A buffer spring is provided between the front cushion and the barrel. Whereby, during the reciprocation of the piston, the valve hole can be reliably closed by the rear cushion under the force of the valve spring. Thus, the pneumatic greaser can during operation stably and continuously eject grease with a low impact.