Abstract: Objective:This study was carried out to obtain high yield chitosanase producing strain.Methods: Chitosanase producing strains were enriched by sole carbon source, and rescreened by observing hydrolysis circle on chitosan plate and assaying culture supernatant enzyme activity.The 16S rDNA gene was amplified by polymerase chain reaction (PCR) for strain identification.SDS-PAGE gel in situ refolding was used for crude enzyme analysis.Single-factor method was adopted to optimizing the fermentation parameters to maximize chitosanase activity.Results:Strain QD1 with high chitosanase activity was isolated from marine environment.Based on the 16S rDNA sequence, QD1 was assessed to be Renibacterium sp., and was thus named Renibacterium sp.QD1.A chitosanase with the molecular weight of about 25ku was observed on refolded SDS-PAGE gel.After optimization, the yield of chitosanase activity reached up to 400U/mL, which was nearly four times of the previous reported chitosanase from Microbacterium sp.QD1.The fermentation medium including chitosan (0.50%) 、KH2PO4 (0.10%) 、K2HPO4 (0.20%) 、MgSO4 (0.07%) 、NaCl (0.10%) 、CaCl2 (0.01%) , yeast extract (0.05%) , potato starch (%) and peptone (0.2%) .Conclusion:A strain with high chitosanase activity was isolated from marine environment which provided a new tool for chitooligosaccharides preparation.