K2CO3 loaded hydrotalcite catalyst was prepared by impregnation method and the condition of preparing catalyst with K2CO3 loaded 20%, blend temperature 80℃,roasting temperature 600℃ and roasting time 6h was confirmed. Biodiesel was prepared from rapeseed oil by transesterification with the solid base catalyst of K2CO3 loaded hydrotalcite. Factors that affected the reaction’s conversion like reaction temperature, molar ratio of methanol to oil, mass ratio of catalyst to oil and reaction time were investigated. The content of methyl ester was analyzed by GC. The conversion of 96.9% was achieved using a 12 methanol to oil molar ratio at 60℃ for 60min and 4% catalyst. The catalytic activity is closely related with its formation of new crystalline phase by the method of XRD and TG analysis.