Objective To investigate protective effect of aqueous extracts of Ocimum basilicum L. (OBL) on adriamycin-induced cardiotoxicity. Methods Fifty Wistar rats were divided into five groups randomly receiving intragastric normal saline (control group and ADR group), 75, 150, 300 mg/kg OBL (OBL groups) once a day for 11 d. Simultaneously, ADR group and three OBL groups were intraperitoneally administered with 5 mg/kg ADR every other day, totally five times. Two hours later after the last dosage, the rat hearts were surgically removed, then myocardial glutathione peroxidase (GSH-Px) activity, superoxide dismutase (SOD) and malondialdehyde (MDA) content were determined and the myocardial ultrastructure was observed under electron microscope. Results Compared with control, MDA was increased (P