There is an increasing commercial demand for nanoparticles due to their wide applicability areas such as electronics, chemistry, catalysis, energy and medicine. Metallic nanoparticles are traditionally synthesized by wet -chemical techniques, where the chemicals used are quit toxic and inflammable. In the present report, bio-reduction of silver nitrate into silver nanoparticles using the plant of Moringa oleifera barks is reported. The synthesized silver nanoparticles are characterized by XRD, FTIR, UV-visible and antimicrobial activity analysis. From the XRD analysis it is found that the synthesized silver nanoparticles were the Face Centered Cubic structure and the crystalline size of the sample is 22.08 nm. FTIR data proved that the components in Moringa oleifera barks act as good reductants and stabilizers for the silver nanoparticles. The absorption in the visible region and broad peak at 480 nm was studied by UV studies. The antimicrobial activity of bio-synthesized silver nanoparticles was analyzed against E.coli and Staphylococcus bacteria. The results revealed that the bark extract is a very good bio reductant for the synthesis of silver nanoparticles.