Abstract: Different components of Oscillatoria chlorina, including whole cells, crude extracts of cells and cell-free culture medium were injected into Litopenaeus vannamei to study the lethal effect. For the toxicity of crude extracts, the effects of cell concentration and water temperature were evaluated, and toxin of crude extracts was analyzed. The results show that O.chlorina cells and crude extracts could cause massive death of shrimp (death rate≥93.72%), while cell-free culture medium had no effect on the survival of shrimp. The toxicity of crude extracts on shrimp was closely related with cells concentration and water temperature. High concentrations of crude extracts (≥2.52 mg · mL^-1) could cause high death rate of shrimp (≥86.67%), and as the concentration dropped below 0.504 mg · mL^-1, the death rate also decreased to 2.22%. The death rate of shrimp injected by crude extracts was 97.8% at 34 ℃, which was much greater than that at 22 ℃(20.0%). The crude extracts did not contain microcystin-RR/YR/LR (MC-RR/YR/LR) by the detection of High Performance Liquid Chromatography(HPLC). In conclusion, O.chlorina had acute toxic effect on L.vannamei, which was closely related with cells concentration and water temperature. The toxin mostly existed in crude extracts of O.chlorina, but was not MC-RR/YR/LR.