Abstract: OBJECTIVE Through microwave irradiation caused the cells ruptured, and then monocrotaline in Crotalaria sessiliflora L was extracted by solvent reflux method to improve extraction yield of the alkaloid. METHODS The material of crotalaria Sessiliflora L containing a certain amount of water was irradiated by microwave. Using methanol as solvent, monocrotaline was extracted and determined by high performance liquid chromatography. RESULTS Optimum experimental conditions ware: 80 mesh of particle size, 21.0 mL of water volume added, 40% of microwave power, 2 minutes of irradiation time, 80 ℃ of extraction temperature, 2 h of extraction time and 1:20 of ratio of material to solvent. CONCLUSION The extraction of monocrotaline in Crotalaria Sessiliflora L was performed successfully by using microwave irradiation couple to solvent reflux extraction. The alkaloid yield was higher than conventional solvent reflux extraction and ultrasonic extraction, and the method is simple, easy to operate.