There　were　many　research　reports　about　microcystins,　a　most　common　algal　toxin　in　eutrophic　freshwater　body.　It　is　a　class　of　monocyclic　heptapeptides　with　many　different　isomerides.　It　has　become　potential　hazardous　material　in　aquatic　environment　for　its　toxic　and　distribution.　This　paper　summarized　the　molecular　structure,　physical　and　chemical　characteristics　of　microcystins　as　well　as　its　pollution　condition.　The　toxic　effect　and　mechanisms　of　microcystins　are　reviewed　too.