In this study, chitooligosaccharides were prepared from cicada slough of Cryptotympana atrata Fabricius by hydrolysis using hydrogen peroxide (H 2 O 2 ). Factors affecting the hydrolysis of chitosan were investigated and the optimum hydrolysis conditions were as follows: time, 4h; temperature, 65°C; amount of H 2 O 2 , 2% (v/v); and pH, 5. Under these conditions, the average degree of polymerisation decreased to ∼4.5. The Fourier transform infrared spectra and product sugar composition indicate that there were no significant chemical changes in the backbones of the chitosan treated with H 2 O 2 .The chitooligosaccharides had high antibacterial activity against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli at the concentration of 100mg/mL.