Abstract: ObjectiveIn order to explain the toxic mechanism of organic extract and cyanobacteria extract from water body.MethodsThe cytotoxicity of these two substances to mouse BALB/c 3T3 cell line in culture was investigated from multiendpoint.The MTT and neutral red intake microassays and microscopic observation were used respectively.ResultsThe rate of viability decreased,which was dose-time-dependent effect relationship on organic extracts concentration.The cell concentration increased following exposure to cyanobacteria extract at low concentration and short time.In contrary,it decreased athigh concentration and long time exposure.Morphological alteration was observed when cell was treated with two substances at comparatively high concentration.ConclusionsToxicity of organic extracts and cyanobacteria extract on 3T3 cell was assessed sensitively by two microassays.Organic extract was harmful on cell membrane and mitochondrion.Cyanobacteria extract can injure the cell membrane,and ithad dual role on mitochondrion,one was irritated,and the other was injury.