In recent years, the excessive reproduction of harmful algae caused by the eutrophication of freshwater and the consequent algal toxin contamination have been widely studied worldwide. Microcystins (MCs), toxic metabolites produced by algae such as Microcystis and Anabaena, are widely distributed, and have stable structure and high toxicity. MCs can enter the human body through drinking water, aquatic products and crops, and have toxic effects on the liver, kidney, reproductive system and nervous system, posing a serious threat to human health. In this paper, the toxicity and mechanism of action of MCs are summarized and analyzed. We believe that this review can provide valuable information for preventing and controlling MCs from causing any harm to human health. © 2020, China Food Publishing Company. All right reserved.