In vitro anticancer potential of methanolic and aqueous extracts of whole plants of Mentha arvensis, M. longifolia, M. spicata and M. viridis at concentration of 100 μg/ml was evaluated against eight human cancer cell lines--A-549, COLO-205, HCT-116, MCF-7, NCI-H322, PC-3, THP-1 and U-87MG from six different origins (breast, colon, glioblastoma, lung, leukemia and prostate) using sulphorhodamine blue (SRB) assay. Methanolic extracts of above-mentioned Mentha Spp. displayed anti-proliferative effect in the range of 70-97% against four human cancer cell lines, namely COLO-205, MCF-7, NCI-H322 and THP-1; however, aqueous extracts were found to be active against HCT-116 and PC-3. The results indicate that Mentha Spp. contain certain constituents with cytotoxic properties which may find use in developing anticancer agents.