Abstract: Eutrophication of freshwater bodies may lead to cyanobacterial blooms. Microcystins(MCs) are secondary metabolites produced by cyanobacteria. The hepatotoxicity and potential carcinogenic activity of MCs have been studied extensively, meanwhile, various adverse effects on immune system have been observed in vivo and in vitro. The immune stimulation of MCs altered immunoregulatory activity and induced immunotoxicity. Long-term exposure at low levels may have an important effect on the immune system in humans and animals. This review focuses on previous in vivo and in vitro studies of MCs immunotoxicity, the current state of knowledge and research needs are also discussed with a summary of the existing important information. The article is aimed to provide reference for environmental health researchers, facilitate the study on relevant mechanisms and the future investigation of potential relationship between exposure and immune-related disease, and offer advices in environmental health management decision making.