A device for reducing fuel dilution of a diesel engine may include an engine oil level sensor mounted to an oil pan for storing engine oil, to sense a level of the engine oil, a heater switch switched on by a signal of a controller, when the level of the engine oil in the oil pan is increased to a reference level or more by fuel diluted in the engine oil, and a heater connected to the heater switch in the oil pan, to evaporate the fuel diluted in the engine oil while being operated by an on state of the heater switch.