The optimized preparation conditions of the concentration of IgG in yak blood after salting out of saturated ammonium sulfate by single factor experiments, including the selection of the hydrolysis time, pH, temperature and the amount of enzyme, as well as the Central Composite experiment, was investigated in this study. The activity of IgG was detected by ELISA and analyzed by using the Response Surface analysis (RSA). The results showed that the optimal concentration of IgG was 27.13 mg/mL when hydrolyzed for at 39 ℃ for 2 h, and enzymolyzed at pH 4.4,