Biodiesel fuel (BDF) can be effectively used as an alternative fuel in diesel engines. The BDF, however, may affect performance and exhaust emissions of the diesel engine because it's physical and chemical properties are different with from the diesel fuel such as viscosity, compressibility and so on. To investigate an effect of injection timing on characteristics of performance and exhaust emissions with the BDF in an IDI diesel engine, this research applied the BDF derived from soybean oil in this study. The engine was operated with six different injection timings from TDC to BTDC 12 ˚CA and six different loads at the engine speed of 1500 and 2000 rpm. In less then the BDF 20, it showed the similar trend compare to the diesel fuel. But, the best injection timing was 2˚CA retarded compare to the diesel fuel with BDF 50.