Hot-water fish protein(HFP),enzymatic fish protein(EFP),acid soluble fish protein(AFP) and alkaline soluble fish protein(ALFP) were prepared by heating extraction,enzyme hydrolysis,acid/alkaline solubilization-isoelectric precipitation from Tilapia head.Nutritional characteristics,solubility and emulsifying properties of these proteins were determined.The protein content of ALFP and AFP was found to be 89.97% and 85.87%,respectively.Total essential amino acids were about 49.72% and 48.63% of the total amino,respectively.The content of crude fat and ash and degree of whiteness of these proteins are significantly lower than that of HFP or EFP(P<0.05).In the pH range 2.0 to 10.0,EFP and HFP were found to have a high solubility of > 93%,at the same time,a low emulsifying activity and less stability were observed.In contrast,solubility of AFP and ALFP is very sensitive to pH.In pH range 4.0 to 6.0,their solubility and emulsifying properties were poor,but these properties are greatly improved when pH is in the range of 4.0 to 6.0.The emulsifying activity index and emulsifying stability index of AFP and ALFP were significantly higher than that of HFP and EFP.These results indicated that fish protein having better nutritional characteristics and emulsifying properties could be prepared by acid/alkaline solubilization-isoelectric precipitation.