Chitosan is a kind of macromolecular polymer with rich source， which has a wide range of application value in many fields， such as chemical industry， food， biology and so on. However， it needs to be degraded into small molecular oligosaccharides to give full play to its activity. As the advantages of enzymatic degradation of chitosan are more and more obvious compared with other methods， the exploration of new stable and efficient chitosanase has attracted the attention of the majority of researchers. According to the chitosanase's amino acid sequence of Bacillus nakamurai in genebank database， we designed the corresponding coding gene and expressed and purified the recombinant protein by E.coli prokaryotic expression system. The results of enzymatic properties showed that the optimum temperature was 37 ℃ and the relative enzyme activity was still 50% after 30 min treatment at 46 ℃， and the optimum pH was 4.5， and 60% relative enzyme activity could be maintained after 60 min treatment at pH 2.5. Ag+ and Hg+ completely inhibited the enzyme activity. Mn2+， Mg2+ and Ca2+ promoted the enzyme activity， while K+， Na+ and EDTA had no obvious effect on the enzyme activity. In this study， the enzymatic properties of chitosanase from B. nakamurai were studied for the first time， which expanded the resources of chitosanase library and provided theoretical basis for the subsequent research and practical application of the enzyme.