Abstract: Compare three different methods of purifying Immunoglobulin G from swine serum with their purifying effect. Octanoic acid precipitation method，ammonium sulfate by-step precipitation method and octanoic acid-ammonium sulfate coprecipitation method are used to purify IgG from swine serum respectively. SDS-PAGE, Bradford kit and AlphaEaseFC software are used to monitor the purity and yield of extract from serum. In the process of purifying IgG, the octanoic acid precipitation method needs shortest time, only 1 hour. But the purity of extract is lowest ,thus the yield is high . The purity and yield of extract by ammonium sulfate by-step precipitation method are higher, but the time is longer. Meanwhile, the octanoic acid-ammonium sulfate coprecipitation method gains the purest IgG, but the time is longest and the yield is lowest. The three kinds of methods have their own features individually, they can be adopted in different condition and need.