Novel series of benzimidazole has been synthesizedand evaluated for their anti-proliferative activity against human breast adenocarcinoma MCF-7, human lung carcinoma A549 and human epitheloid cervix carcinoma HELA. Some derivatives showed potent growth inhibitory activity, in particular compounds 4a, 4b, 5a and 7b. N-(1H-benzimidazo-2-yl)-2-(1H-benzimidazo-2-ylamino)acetamide 5a was found to be the most potent with percentage inhibition 95% on MCF-7 cell line and 77% on A549 cell line compared to 60% inhibition of cisplatin. The antitumor activity of 5a was accompanied by significant increase in the activity of superoxide dismutase with concomitant decrease in the activities of catalase, glutathione peroxidase and reduced glutathione level. Accordingly, the overproduction of hydrogen peroxide and nitric oxide allowed Reactive Oxygen Species (ROS)-mediated tumour cells death, as monitored by reduction in the synthesis of protein and nucleic acids.