Conventionally physical and chemical methods are used for the biosynthesis of silver nanoparticles. Biological methods of nanoparticles synthesis are cost effective, easily scaled up and environmental friendly. A green synthesis of silver nanoparticles has been achieved using environmentally acceptable plant extract. It was observed that Moringa oleifera Lam leaf extract can reduce silver ions into silver nanoparticles at room temperature. The synthesized nanoparticles have been characterized by the UV–visible spectroscopy, high resolution transmission electron microscopy. Further, the antibacterial activity of silver nanoparticles was evaluated by well diffusion method and it was found that the biogenic silver nanoparticles have antibacterial activity against Pantoea agglomerans (27mm) followed by Ralstonia solanacearum, Erwinia amylovora and Pseudomonas lachrymans (19.66 mm, 16.66 mm and 13 mm, respectively) and the lowest for Agrobacterium tumefaciens and no effect on Erwinia carotovora compared to control. Investigation on the antibacterial activity of synthesized silver nanoparticles against some phytopathogenic bacteria reveals high potential as antibacterial agent in controlling various plant diseases caused by bacteria.