The present study reports an environmental friendly method for the synthesis of silver nanoparticles (Ag NPs) using an aqueous extract of Acacia auriculiformis that acts as reducing agent as well as capping agent. The obtained NPs were characterized by UV-vis absorption spectroscopy and showed a sharp surface plasmon absorption band at ∼400 nm. Fourier transform infrared spectroscopy (FTIR) showed nanoparticles were capped with plant compounds. Transmission electron microscopy (TEM) showed that the particles were spherical in nature with diameter ranging from 20 to 150 nm depending on the pH of the solution. The as-synthesized Ag NPs showed antibacterial activity against both Gram negative and Gram positive bacteria with more efficacy against Gram negative bacteria.