Abstract: The high-efficiency microcystin-LR-degrading strain Pseudomonadaceae M26,which isolated from the sediment of eutrophic reservoir in Fuzhou,China,for the biodegradation of MCLR was investigated.We studied the influence of inoculum concentration,temperature,aeration,pH and initial concentration of MCLR on MCLR degradation by Pseudomonadaceae M-6.It was shown that the biodegradation rates could be reached to 90% at 10% inoculum concentration,pH 7.0,30℃,and aeration speed of 150 r/min after 6 days.The MCLR degradation rates were also affected by the initial concentrations of MCLR owing to the effect of the absorption of nitrogen and carbon sources by Pseudomonadaceae M-6.The 6-day biodegradation rate was more than 95% when the initial MCLR concentration was 15.2 mg/L.From SDS electrophoresis,it can be concluded that the MCLR biodegradation was mainly due to the three kinds of enzymes which were all intracellular enzymes.