Abstract: Factors affecting the emulsion stability of the inactivated type 2 porcine circovirus vaccine were investigated. The pH, speed and time applied in the emulsification process were varied to compare the stability of the emulsion in the aspects of viscosity, particle size and storage temperature. The results showed that the emulsion was most stable at pH 7.0-7.5 with high shear and short mixing time. Within a limit, prolonged shearing would increase the stability but also raised the viscosity of the resulting emulsion. It was concluded that the optimal conditions to emulsify the vaccine were pH 7.0-7.5 at 19 000 r·min^-1 for 8 min.It was recommended to keep the pH of antigen at 7.0-7.5 in the production of porcine circovirus vaccine, and determine the speed and time of emulsification according to different equipment to keep the vaccine stable.