The HeLa and MCF-7 cells were treated with Methanolic extract of Argemone Mexicana Linn. and effects on the cytotoxic nature of extract of Argemone Mexicana Linn. Were determined using Trypan blue and Hoechst tests. The MTT assay results were used to evaluate the anti-cancerous activity of the extract.The effects of plant leaves extract on cancer cells was studied. The IC<inf>50</inf> (1.35μg/μl to 1.2μg/μl.) values was found for the extract.The nature of cytotoxic activity is found to be apoptotic rather than necrosis by Hoechst test. The anti cancer effects of methanol extract of Argemone Mexicana Linn.leaves may be related to their content of flavonoids. This study validates the traditional use of the plant in management of Cancer. © 2011 Elsevier B.V., All rights reserved.