The antioxidant activities of betaine were evaluated by cellular antioxidant activity assay, AAPH-induced erythrocyte assay, and AAPH-induced liver cell assay. The results revealed that betaine (200 mmol/L) treatment effectively reduced AAPH-induced erythrocyte hemolysis by 54.19%, and the MDA content by 4.32 nmol/mg. Erythrocytes induced by AAPH was appeared shrinking under scanning electron microscope, however, erythrocytes prior treated with betaine was only presented slight shrinking. Moreover, after beanie treatment, the amount of ROS in AAPH-induced erythrocytes declined by 57.16 IU/mg, and the activities of SOD, CAT, and GPx decreased by 9.84 mU/mg, 13.91 mU/mg, and 43.59 mU/mg, which were same as the normal levels. The betaine (50 mmol/L) treated in liver cell after AAPH-induced, MDA level was dropped by 0.21 nmol/mg and the SOD and CAT activities decreased by 173.21 U/mg and 53.9 U/mg, which had no significant difference with the normal cell. In conclusion, betaine could protect cells from the damage of radical induced by AAPH, showing that betaine has good antioxidant activities.