Chitooligosaccharides have important application value in the fields of food and agriculture. Chitosanase can degrade chitosan to obtain chitooligosaccharides. The marine metagenome contains many genes related to the degradation of chitosan. However, it is difficult to mine valuable genes from large gene resources. This study proposes a method to screen chitosanases directly from the marine metagenome. Chitosanase genechis1754was identified from the metagenome and heterologously expressed inEscherichia coli. The optimal temperature and pH of CHIS1754 were 55 degrees C and 5.5, respectively. A mutant, CHIS1754T, with 15 single point mutations designed based on molecular evolution data was also expressed inE. coli. The results indicated that the thermal stability of CHIS1754T was significantly improved, as theT(m)showed an increase of similar to 7.63 degrees C. Additionally, thek(cat)/K(m)of CHIS1754T was 4.8-fold higher than that of the wild type. This research provides new theories and foundations for the excavation, modification, and industrial application of chitosanases.