Abstract: In order to improve that utilization rate and added value of seafood wastes such as shrimp and crab. The chitinase-producing strain GXUN-20 was isolated, purified and screened from the mudflat sediments(shrimp, crab and shell wastes) near Damenhai Duck Farm in Hepu county, Guangxi Province. After physiological and biochemical identification and the construction of phylogenetic tree based on 16S rDNA sequence, the strain was preliminarily identified as Lysobacter firmicutimachus. Taking chitinase activity as index, the single factors optimization of fermentation conditions were conducted for strain GXUN-20. On the basis of four factors(nitrogen source concentration, initial pH of fermentation broth, chitin powder concentration and inoculation amount) that had significant results in the single factor optimization, four levels of orthogonal experiment and variance analysis of orthogonal experiment were carried out. The results showed that the concentration of nitrogen source had a significant effect on enzyme production(P=0.013<0.05). When the nitrogen source was 1 g/L soybean cake powder, chitin powder was 20 g/L, the inoculation amount was 3%, the initial pH of the fermentation broth was 8.4, and the fermentation temperature was 30 ℃and 200 r/min for 6 days, the chitinase activity in the fermentation broth reached the maximum value of 0.965 U/mL, which was 6.89 times of the enzyme activity before optimization. The results of this study would provide the basic data and experimental methods for the further development and application of the chitinase produced by GXUN-20 strain.