A promising bacterial strain that has a strong ability in the bildegradation of micrlcystins(MCs)was isolated from the sediments of Dianchi Lake and identified as Delftia acidovorans by The Instiute of Mictobiology, Chinese Academy of Science. MC-RRand LRat initial concentrations of 92.8 mg/L and 40.6 mg/L were completely biodegaded by D. acidovorans in 3 days and the average biodegradation rates of MC-RR and LR per day were 46.4 mg/L and 20.3 mg/L, respectively. It was showed that the growth of D. acidovorans was pronoted however the biodegradation of MCs could mnot be improved in the presences of other carbon and nitrogen containing compounds. Itwas also indicated that the biodegradation of MCs could not be accelerated with mtal ions of Cu2 , Mn2 and Zn2 . This research was very important in both the basic biodegradation and the application in the trestment of MCs in water body.