In recent years there has been a substantial increase in the use of functional foods for disease control. Fruits and vegetables produce phytochemicals such as flavonoids and antioxidants which can lower oxidative stress and reduce the risk of chronic ailments like cancer. The aim of the present study was to investigate the antioxidant capacity and the possible protective effects of Amaranthus paniculatus leaves on the antioxidant defense system in Ehrlich's ascites carcinoma (EAC) -treated mice. Oral administration of the leaf extract at different doses caused a significant decrease in tumor volume, viable cell count and tumor weight and elevated the life span of EAC bearing mice. It also showed an improved antioxidant potential as evidenced by a significant increase in the cellular antioxidant defense system such as catalase, superoxide dismutase and reduced glutathione and also significantly reduced the levels of TBARS. The levels of RBC, hemoglobin and lymphocyte count were altered in EAC bearing mice and were reverted back to near normal levels after the treatment with the leaf extracts. Their adequate content of total phenolics and flavonoids, DPPH scavenging activity which further suggests that the extracts exert a significant protection against oxidative stress conditions.