Abstract: A pneumatic oil lubricator for lubricating replenishment mainly has a pneumatic oil pump for pumping oil from a oil reservoir to an oil outlet unit, such as an oil gun. An automatic controlling apparatus is provided which has a hollow unit sleeve, a piston disposed in the hollow unit sleeve, and a spring mounted on the piston. The piston has interior air passage formed at one end thereof. The entrance and the exit of the interior air passage are faced to the second connecting inlet and the connecting outlet respectively. In which, the hollow sleeve has a first and a second connecting inlets at its two end and an connection outlet. The first connecting inlet is linked to an air compressor, the first connecting outlet is linked to the air outlet unit, and the connecting outlet is linked to an air inlet of the pneumatic oil pump.