Abstract: The solid base catalyst K₂CO₃/Al₂O₃ was prepared by impregnation method. The factors to influence the reaction activity of producing biodiesel from waste cooking oil including the loading of active component K₂CO₃ on the catalyst, the roasting temperature and the roasting time were investigated. The catalysts were characterized by FT-IR, XRD, TG-DTG, SEM and BET techniques. The results show that the catalyst exhibits an excellent catalytic activity for the transesterification of waste cooking oil to biodiesel. The solid base catalyst loaded with 50% K₂CO₃ and calcinated at 500 ℃ for 3 h exhibits a high catalytic activity for the transesterification, and the yield of biodiesel reaches 86.70%. The characterization reveals that the catalyst activity of K₂CO₃/Al₂O₃ is associated with the formation of new crystalline phase due to the interaction between K₂CO₃ and Al₂O₃ during calcination. After the catalyst is reused for 4 times, the yield of biodiesel is still above 75%. The main quality indexes of the product can reach the biodiesel B100 standard completely.