The solid superacid catalyst SO42-/ZrO2 was prepared by impregnation and characterized by infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. Their performances were evaluated by the transesterification reaction of waste cooking oil (WCO) with methanol. The influence of the load ratio of SO42-/ZrO2, molar ratio of methanol/waste cooking oil, catalyst amount, reaction temperature, and reaction time on biodiesel yield was investigated. Under a condition of methanol/WCO molar ratio of 9:1, a catalyst amount of 3 wt %, reaction time of 4 h, and reaction temperature of 120 degrees C, 93.6% of biodiesel yield was obtained.