The influence of soybean biodiesel on vibration characteristics and noise emissions of a three cylinder, four stroke, direct injection diesel engine has been experimentally investigated in the present work. Two types of soybean biodiesel were produced via transesterification method using sodium hydroxide and sodium methylat as catalysts. Fuel properties of biodiesel fuels were observed similar to diesel fuel specifications. A high sensitivity electronic vibration analysis system was developed for measurement of frequency spectrum of diesel engine vibration. In comparison with diesel fuel, vibration of engine with the biodiesel fuel has the lower amplitude and lower frequency. Similar results were obtained with both of the two biodiesel fuels. Noise emission of diesel engine showed a decreasing trend with biodiesel fuel.