As the variety of microorganisms and more and more antibioticsª²resistant bacteria are identified, the treatment of bacterial and viral infections have become less effective in recent years, and exploring a new antimicrobial therapy is imperative. Photodynamic antimicrobial chemotherapy (PACT) is a new antiª²infection method with the similar principle of photodynamic therapy that utilizes light of an appropriate wavelength to excite the nontoxic photosensitizers which selectively target tissue cells, in the presence of oxygen, generates reactive oxygen species and leads to a series of photochemical reactions which are responsible for the killing of microbial cells nearby.  PACT is an effective method for treating the infections caused by bacteria, fungi, or viruses, especially for the antibioticsª²resistant infections. In this paper, we will give an overview of current knowledge regarding the classification of photosensitizer.