The effect of emulsifier S1170(sucrose ester) on particle size distribution,protein concentration in aqueous phase,surface sucrose ester concentration,partial coalescence of fat globule and creaming rate of emulsion stabilized by caseins were investigated.The possible mechanism for the stability of casein emulsion affected by sucrose ester content was also analyzed.The results indicated that with increasing of sucrose ester content,the protein concentration in aqueous phase and surface sucrose ester concentration were increasing,the fat part of the coalescence rate was gradually decreasing,the droplet size and the creaming rate were decreasing,which in turn stabilized the emulsions.The partial coalescence of fat globule decreased slowly,while the creaming rate increased slowly to the dynamic equilibrium value.In summary,the stability of emulsion was the best at sucrose ester content of 0.60%.