A fuel filter for a diesel engine may include an upper cover forming inflow and outflow passages of diesel fuel, a housing integrally mounted in a vehicle body, coupled to the upper cover and housing a filter assembly, and a body penetrating a central portion of the filter assembly, disposed between the upper cover and the filter assembly and integrally forming the upper cover, a heater assembly, and a moisture sensor, in which the heater assembly may be configured to selectively operate according to a detection signal of a fuel temperature sensor that is provided in the engine body.