【Objective】The present study was carried out to explore the effect of chitosan oligosaccharide on secondary metabolites and some defense enzyme activities related to stress resistance in sugarcane. 【Method】The leaves of sugarcane variety ROC22 were treated with 0 （CK）， 25， 50 and 75 mg/L chitosan oligosaccharide solution at the early elongation stage. The polyphenol content and the activities of defense enzymes， viz.， phenylalanine ammonialyase （PAL）， polyphenol oxidase （PPO） and peroxidase （POD） were measured in +1 leaf of sugarcane at 1， 2， 3 and 4 d after spraying. 【Result】50-75 mg/L chitosan oligosaccharide treatment was conducive to the accumulation of polyphenol in sugarcane leaf. The PAL activity reached to its maximum and was 1.78 times higher than the control after 2 d of 50 mg/L chitosan oligosaccharide treatment. The PPO activity reached to its maximum and was 1.7 times higher than the control after 4 d of 50 mg/L chitosan oligosaccharide treatment. The 75 mg/L chitosan oligosaccharide treatment was conducive to improve POD activity of sugarcane leaf. 【Conclusion】It was found that 50-75 mg/L chitosan oligosaccharide treatment can improve the polyphenol accumulation and the activities of defense enzymes in sugarcane leaves， which is helpful for improving sugarcane resistance to various biotic and abiotic stresses.