Abstract: To explore the changes in physicochemical characteristics of muscle protein of grass carp during cold storage, the muscle protein samples were prepared from the grass carp fillets which were refrigerated at 4 ℃ for 0, 2, 4, 6, 8 and 10 d, respectively. And their molecular weight (MW) distribution, water holding capacity（WHC）, solution viscosity, thermodynamic property, as well as salt solubility of actomyosin were determined by size exclusion HPLC, rheometer and differential scanning calorimetry (DSC), etc. The results showed that the average MW of muscle protein was decreased during the whole cold storage period, while the WHC decreased severely in the early stage of cold storage and was dropped by 56.12% at the 8th day. The apparent viscosity of muscle protein decreased quickly at low shear rates, and fell from 0.89 Pa·s of 0 d to 0.05 Pa·s of 10 d at a shear rate of 20 s⁻¹. The salt solubility of actomyosin declined obviously and dropped by 40.96% after 6 d of cold storage. Moreover, two endothermic peaks were observed in DSC curves of the protein samples from refrigerated fish muscles, and the onset temperature (T_e) and peak temperature (T_m) of the biggest peak were both maximized at the 6th day, while its corresponding enthalpy change (∆H) was minimized. The results indicated that the 6th day of cold storage was a key time point for complex changes of grass carp muscle proteins. This study provides basic data for better understanding the deterioration mechanism of grass carp muscle during cold storage.