The anaerobic decomposition of high-density cyanobacteria and the kinetics of contaminants release were investigated based on a set of batch tests in this study.The results showed that the degradation rates of chlorophyll-a(Chl.a were 0.074, 0.133,and 0.081 d^-1,respectively,at different cyanobacterial densities of 2.23×10¹²,1.19×10¹³ and 4.47×10¹³ cells/L, respectively.The chemical oxygen demand increased while the UV₂₅₄ value increased initially and then decreased,suggesting that the release of organic compounds increased,but the molecules of which were reduced gradually during the degraded process.Accordingly, the pH of incubation solution remained acidic and the conductance increased,up to 949 μS/cm.The decomposition of cyanobacteria resulted in a high release of nitrogen and phosphorus.Moreover,dissolved organic nitrogen was degraded gradually into inorganic nitrogen form,in which the amount of ammonia nitrogen accounts for 90%.The results demonstrate that the anaerobic decomposition of high-density cyanobacteria can release a large amount of organic compounds and nutrients into water,furthermore the release of contaminants increases with the increasing density of cyanobacteria.Therefore,to avoid high-density cyanobacteria deteriorating water quality and even threatening drinking water safety,we need to remove cyanobacteria timely when algal bloom occurs in the lake which is served as water resource.