Interaction of silver nanoparticles with bacterium depends on their size and shape. Although many studies have been recently done about synthesis and investigating reaction of spherical silver nanoparticles to bacterium, few studies have been performed in terms of shape of such nanoparticles. In this research, triangular structure nanosilver particles were synthesized and their antibacterial behavior on three conventional bacterium i.e. Escherichia Coli, Staphylococcus aureus and Pseudomonas aeruginosa were assessed. At first, silver nitrate solution and deionized water in the presence of polyvinyl pyrrolidone were prepared. Sodium citrate and sodium borohydrate were then added to the solution. Hydrogen peroxide acted as an oxidizing agent. Transmission Electron Microscope (TEM) analysis showed that distribution of triangular shaped nanosilver particle size was broad and in the range of 7-65 nm. This triangular formed nanosilver had a sharp edges and vertexes. The UV spectroscopy of blue-color solution showed two peaks in the range of 331nm and 627 nm which reflected anisotropic and the formation of triangular structure of silver nanoparticles. The halo test results represented that halo diameter for gram positive S. aureus was smaller than the other gram negative bacterium.