Objective: To synthesize silver nanoparticles from leaves extract of Hydnocarpus Pentandra (H. Pentandra) and test the anti-cancer activity of synthesized silver nanoparticles against breast cancer cell line (MCF-7 cells). Method: Ten milliliter of leaves extract was mixed with 10 mL of aqueous 1 mM silver nitrate solution and kept in an incubator shaker system at 37 ºC for 24 hours. During this period, yellowish to reddish-brown color changes was observed. Characterization of silver nanoparticles using UV-vis spectrophotometry and SEM analysis were performed. Antioxidant activity of silver nanoparticles was performed using DPPH method. Anti-cancer activity of silver nanoparticles was tested using in vitro cytotoxicity test with 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide against MCF-7 breast cancer cells. Results: UV-vis spectral analysis indicated the sliver surface plasmon resonance band at 438 nm. SEM analysis showed that silver nanoparticles to be spherical in shape with a size in the range of 141 nm to 202 nm. The synthesized silver nanoparticles exhibited antioxidant activity at dose dependent manner using DPPH method. The synthesized silver nanoparticles efficiently reduced the viability of MCF-7 breast cancer cells in a dose dependent manner. Conclusion: It has been demonstrated that the leaves extract of Hydnocarpus Pentandra could produce silver nanoparticles and the silver nanoparticles are quite stable in solution. Further studies are needed to characterize the mechanism involved with anti-cancer activity of the silver nanoparticles.