Chitosanase (EC3.2.1.132) catalyses the hydrolysis of the β-1,4 glycosidic bonds in chitosan to produce physiologically active chitooligosaccharides, polyglucosamines with 2 to 10 degrees of polymerization. It has been found in many microorganisms including bacteria and fungi. 51 chitosanaseproducing strains were screened and isolated from 11 soilsamples rich in shrimp and crab shells by transparent circles in the culture media containing chitosan as sole carbon source. After screening of flatpanel, flaskshaking cultivation and enzyme kinetics in fermentation, a strain (H₂) with higher chitosanlytic activity was acquired. According to its morphological, cultural, biochemical and physiological characteristics and phylogenetic analysis of 16S rDNA, the strain was identified and named as Streptomyces roseolus DH. Further studies of fermentation conditions showed that the optimum temperature and initial pH of medium were 30 ℃ and 7.2, respectively. Moreover, the colloid chitosan (1.0%) and peptone (0.5%) were chosen as the best carbon and nitrogen sources among the tested ones. Under these conditions, the activity of chitosanase in media reached 6.10±0.12 U/mL after 60hour fermentation. This strain with higher yield of chitosanase and shorter fermentation period displayed good potential for future applications.