Objective: To extract and determine the flavonoids of hawthorn fruits and their antioxidative effect. Method: The ultrasonic method was used for extracting flavonoids. The content of flavonoids was determined by spectrophotometry, and the antioxidation effect was determined by flow-injection chemiluminescence.. Results and Conclution: The recovery rate was 96%~105% and the coefficient of variation was 0.14 % by spectrophotometry. Hawthorn fruits had high antioxidative effect, showing dose-response relation.