Nanotechnology manipulates material at nanoscale (1-100 nm) for its interesting novel properties comparing to those of the materials in macro dimensions. Nanoparticles recieve much interest due to their potential applications in medicine and many other fileds. Silver nanoparticles are commercially available in various antibacterial products while gold nanoparticles show great potential in cancer treatment and diagnositcs. Thus, it is essential to determine possible toxic effects that silver and gold nanoparticles can have on both humans and wildlife. Following that purpose, experiments that have been taken on various different in vitro and in vivo models have shown that silver and gold nanoparticles tend to accumalate in spleen and liver, that they can stimulate immune response and can exert toxic effects depending on the size and capping agents of the particle, as well as on the dose and time of exposure. ROS and RNS production, membrane and DNA damage are some general effects silver and gold nanoparticles can have on cells, although there are many other specific effects that need further investigation. It is believed that silver nanoparticles are more toxic than the gold ones because they oxidize more readily.