Abstract: The aim of the current study was to investigate the changes of the whey protein when the somatic cell count increased and lactose content decreased in milk. Milk was classified into milk with low lactose and high somatic cell count, and control group according to concentration of lactose and somatic cell count in milk. Whey proteins were collected by ultracentrifugation and separated by twodimensional gel electrophoresis, stained with Coomassie Blue G250 solution, and identified by matrix assisted laser desorption ionization time of flight mass spectrometry. βcasein was decreased, while whey proteins including serum albumin, haptoglobin, lactoferrin, transferrin and cathelicidin 1 increased in milk with low lactose and high somatic cell count group. The results suggested that the increase of whey proteins in milk was associated with concentration of low lactose, which may be the defense response of mammary gland to the damage of integrity of mammary gland epithelial cells when lactose content decreased in milk.