Low temperature storage generally induced the symptom of peel browning in Huangguan pear. To solve this problem， this research used different mass fractions of chitosan oligosaccharide (COS) aqueous solution， including 0.25%， 0.5% and 1%， for treating the postharvest Huangguan pear before the low temperature (0 ℃) storage， and investigated the effect of COS on peel browning， reactive oxygen metabolism as well as fruit quality. The results showed that COS treatment could remarkably inhibited the peel browning incidence， especially 0.5% COS. 0.5% COS treatment decreased the incidence and index of peel browning by 89% and 32%， respectively. Due to the increased activities of polyphenoloxidase and lipoxidase， the activities of catalase， ascorbate peroxidase， superoxide dismutase and phenylalnine ammonialyase maintained the higher levels in 0.5% COS-treated fruit peel. Compared to other treatments， 0.5% COS enhanced the higher values of total phenolic and ascorbic acid， while the 0.5% COS reduced the accumulation of hydrogen peroxide and malonaldehyde. Although the COS treatment could improve the levels of soluble solid， titratable acid and firmness， there were not significant. In conclusion， 0.5% COS treatment could reduce the incidence of peel browning and improve fruit quality of Huangguan pear， significantly before the cold storage.