Chemoprevention is an important strategy to control the process of carcinogenesis. The potential of usingmedicinal herbs as cancer chemopreventive nutraceuticals and functional food is promising. Thus, there is aneed for exploring drugs/agents which act as chemopreventive agents. Phyllanthus niruri is a well known medicinalplant which has been used in Ayurvedic medicine as hepatoprotective, antiviral, antibacterial, analgesic,antispasmodic and antidiabetic. The present study was carried out to evaluate the anti-tumor activity of ahydro-alcoholic extract of the whole plant, in 7-9 week old male Swiss albino mice, on the two stage process ofskin carcinogenesis induced by a single topical application of 7, 12-dimethylbenz (a)anthracene (100μg/100μlacetone) and two weeks later promoted by repeated application of croton oil (1% in acetone/three times a week)till the end of experiment (16 weeks). The oral administration of P. niruri at a dose of 1000 mg/kg/b.wt. at peri-(i.e. 7 days before & 7 days after DMBA application) and post- (i.e. starting from the croton oil application)initiational phase of papillomagenesis caused significant reduction in tumor incidence, tumor yield, tumor burdenand cumulative number of papillomas as compared to carcinogen-treated controls. Furthermore, the averagelatent period was significantly increased in the PNE treated group. The results thus suggest that P. niruri extractexhibits significant anti-tumor activity, which supports the traditional medicinal utilization of this plant.