Peroxynitrite is a highly reactive oxidant that has been implicated in a number of serious human diseases including cardiopathy, acute inflammation and cancer. The decomposition of peroxynitrite can be promoted efficiently by metalloporphyrins and are therefore important to detoxify the cytotoxic oxidant as therapeutic agents. A novel cobalt porphyrin was synthesized to investigate the scavenging effect on peroxynitrite decomposition. Kinetics of peroxynitrite decomposition in the presence of cobalt porphyrin was studied by UV-Vis spectrophotometer and stopped flow instrument. The kinetic experiments reveal that cobalt porphyrin could accelerate the decomposition of peroxynitrite and the catalytic ability is improved with the increasing concentration of cobalt porphyrin. The study is helpful to develop more effective scavengers of peroxynitrite in order to treat related diseases.