To prevent unfiltered oil from flowing in a main oil gallery when an oil filter unit is detached.

An oil filter assembly according to one embodiment of the invention includes an oil filter housing, the oil filter unit, and a drain valve unit. The oil filter housing is provided with an oil inlet passage through which oil supplied from an oil pan passes, an oil discharge passage through which the oil discharged to the main oil gallery passes, and an oil drain passage though which the oil discharged to the oil pan passes. The oil filter unit is disposed in the oil filter housing so as to filter impurities contained in the oil flowing into the oil filter housing. The drain valve unit selectively shuts off the oil discharge passage or the oil drain passage, corresponding to attachment/detachment of the oil filter unit.