Green synthesis methods by plant extracts leads to production of metal nanoparticles without using harsh, toxic, and expensive chemicals commonly used in physical/chemical processes. In this study, silver nanoparticles (AgNPs) were prepared easily, fast, cost-effectively and successfully using aqueous galls extract of Quercus infectoria (Q. infectoria) as a reducing and capping agent. The results revealed that AgNPs were highly stable and their morphologies were spherical with an average diameter of about 33 nm. The galls extract and AgNPs showed excellent antibacterial activities toward four types of bacteria. The antioxidant ability of galls extract and AgNPs was evaluated by DPPH assay and showed considerable antioxidant potential. Cytotoxic activity of AgNPs was tested by MTT assay. AgNPs exhibited significant anticancer activity against human breast cancer cells (MCF-7). AgNPs synthesized by Q. infectoria galls extract with high antibacterial, antioxidant and anticancer activity would be favorable systems for bacterial disease and cancer treatment.