Biodiesel is one of the most used renewable energy sources for diesel engines. Blends of diesel and biodiesel usually require additives to improve the lubricity and combustion efficiency. The function of the Mn is to increase the catalyst activity in fuels. Mg addition also increases cetane number and decreases freezing point of fuels. In this study, blends of 50 % No. 2 diesel fuel and 50 % rapeseed oil methyl ester biodiesel (50B) was used as a base fuel. Magnesium additive was doped into the biodiesel blend by 1, 6 and 12 ppm Engine tests were performed with these 3 different fuels in a four -stroke, four cylinder, diesel engine at full load and different engine speeds in a hydraulic dynamometer. Performance and emission parameters of the engine were determined with this experimental study. According to the experimental results, CO, HC and smoke level decreased, however, CO2 and NOx emissions increased.