Cancer is a lethal disease or a destructive phenomenon arises in human beings because of genetic factors or exposure to toxic chemicals or viral infections etc. Radio therapy is very promising in the treatment of cancer compared to other treatments. However normal cells are also destroyed along with tumor cells in this treatment. Application of nanomedicine in the treatment of cancer is a novel approach. From research findings it can be known that MTT assay is generally used and widely accepted method in screening invitro anticancer activity of metal naoparticles. In addition biosynthesized silver nano particles(AgNPs) have exhibited remarkable activity against cancer cell lines in MTT assay. Green synthesized silver nanoparticles inhibit the proliferation of cancer cells by activating the apoptosis process or changing the cellular chemistry. Biosynthesized AgNPs may also block the tumor growth by damaging the function of mitochondria or generaration of ROS. Plants are the natural treasures of secondary metabolites. In the green synthesis these phytochemicals acts as reducing and stabilizing agents of silver nanoparticles. The plant mediated AgNPs have shown dose and time dependant antitumor activity on cancer cells. The present study deals with the nature of different plants used in the synthesis of silver nanoparticles. The review mainly focussed on invitro cytotoxic activity of plant mediated AgNPs on selected cancer cell lines.