The protective effects of Sonchus asper methanol extract (SAME) against KBrO3-induced oxidative damage in heart tissues of rat were determined in this study. Sprague-Dawley male rats (180 to 200 g) were divided into five groups. Group I: received saline (1 ml/kg bw, 0.85% NaCl) and DMSO (1 ml/kg bw); group II: were injected with KBrO3 (20 mg/kg bw, ip); group III and IV: treated with KBrO3 and after 48 with SAME (100; 200 mg/kg bw) and group V: with SAME (200 mg/kg bw). All the treatments were given twice a week for four weeks. The results revealed that KBrO3 induced oxidative stress as evidenced by the significant decrease in the activity levels of antioxidant enzymes (CAT, POD, SOD, GSH-Px, GSR, GST, QR, XO) and glutathione (GSH), while increase in the levels of γ-GT, MDA and H2O2 in cardiac samples compared with the control group. Serum levels of CK, CK-MB, LDH, uric acid, AST, ALT, ALP, triglycerides, total cholesterol, LDL, VLDL were elevated while HDL level was significantly reduced in KBrO3 group compared with the control. Since SAME treatment reversed these responses dose dependently, it seems likely that S. asper methanol extract can protect the cardiac tissues against KBrO3 mediated oxidative damage.