An improved oil conditioning filter, for use with an internal combustion engine, includes a mechanically active filter element and a chemically active filter element having a reactive basic conditioner therein. The reactive basic conditioner is provided to counteract acidic combustion products in lubricating oil in an internal combustion engine. In a preferred embodiment of the invention, the chemically active conditioning agent is provided in a plurality of pellets disposed within the oil filter housing. The pellets may be bonded together to form an integral porous filter element having spaces defined between the pellets thereof. The pellets are made of a mixture including a polymeric binder and the chemically active conditioning agent, in a defined weight ratio and in a narrow range of particle sizes. The chemically active filter element reacts with acids present in the oil to form a product which may be filtered out of the oil. The pellets are made either by a hot extrusion process or by a solvent process.