Abstract: The content of IgG was detected by single immunodiffusion method so as to evaluate the losing degree of IgG caused by preparation and thermal disinfection process of whey, such as degreasing, removing of casein, and so on. As shown by the results, IgG decreased by 4.5 % -11.5 % after the process of degreasing and removing of casein, while IgG decreased by 8.0 %-18.8 % after cold pasteurization. No IgG was detected in the colostrum after the colostrum was treated at（75±2）℃for 15 s and（80±2）℃ for 10 s. And this result is inconsistent with previous reports. No IgG was detected in UHT-treated mature milk. There was interaction between casein acid clotting （to remove casein）and heating procedure, causing more loss of IgG, and the content of IgG was decreased by 2.1%-4.3 % compared with that in chymosin-treated （to remove casein）samples.