In this study, an ecofriendly, green method for synthesis of silver nanoparticles (AgNP) has been developed using Mallotus tetracoccus (MT) leaves as a reducing agent. The formation of AgNPs was standardised at pH 7 and 60 ℃. UV-visible spectroscopy showed the high peak of absorption band at 420 nm. By atomic force microscopic (AFM) and scanning electron microscopic (SEM) observations, the size of the silver nanoparticles was found to be in the range of 46 to 100 nm, with an average size of 73 nm. The energy dispersive x-ray spectroscopic (EDX) profile of silver nanoparticles showed typical optical absorption peak approximately at 3 keV. FTIR spectroscopic study revealed that hydroxyl groups of phenols and carboxylic acids were involved in the formation of AgNPs. Through MTT assay, the cytotoxicity results showed that AgNPs were highly effective on human ductal breast carcinoma cell lines (T47D) (76.8 to 84.9%). Thus, the MT-synthesized NPs are said to possess significant anticancer activity on cancer cells and very less toxicity on normal cells, which suggests its further applications in medicine.