Biodiesel was made from waste oil with solid acid catalyst and microwave irradiation. The effects of the reaction conditions such as reaction temperature, time, microwave power, the molar ratio of ethanol to waste oil and the mount of solid acid on the biodiesel yield were discussed. A quadratic regression models was founded and the process was analyzed by response surface methodology. The results showed that the biodiesel yield is 94.58% as the reaction temperature is 82℃ ,the reaction time is 93 min,the molar ratio of ethanol to waste oil is 7 : 1 ...