A promising bacterial strain for the biodegradation of Microcystins (MCs) was isolated from Dianchi lake in China and identified as Sphingopyxis sp. USTB-05 by the analysis of 16s rDNA Initial MC-RR of 42 3 mg.L-1 was completely degraded by USTB-05 within 36 h, which was a relatively high biodegradation rate of MC-RR With the cell-free extract (CE) of Sphingopyxis sp. USTB-05, MC-RR was biodegraded at a more rapid biodegradation rate compared with its strain, so that initial MC-RR of 42 3 mg.L-1 was completely biodegraded within 10 h During the bio-reaction of MC-RR catalyzed by CE, two intermediate metabolites and a dead-end product of MC-RR were observed on IIPLC profiles and all of them had similar scanning profiles in the wavelength from 200 to 300 nm, indicating that the group of Adda in all products of MC-RR remained intact