Biogenic technique is one of the easy, economic and environment friendly method for the synthesis of Nanoparticles. Cobalt nanoparticles was synthesized by using Strobilanthes urticifolia plant leaves extract as a reducing agent and tin was doped on the synthesized cobalt nanopartilces. The synthesized doped and undoped nanoparticles were characterized by UV-visible spectroscopy, FTIR and Scanning electron Microscopy.