Skimmed milk, caseins and whey proteins isolated from colostrums collected on the first to fifth days postpartum were hydrolyzed by different enzymes (alcalase, flavourzyme, and porcine small-intestinal enzymes). To investigate how different protein hydrolyastes affect cell death, leukemic U937 cells were treated with different protein hydrolysates at 100 - 1000 μg/mL for 24 to 120 hat 37°C in 5% CO2 incubator. The results showed that protein hydrolysates leading to U937 cell death exhibited dose-and-time-dependent characteristics. This study also found that the proteins hydrolyzed by porcine small-intestinal enzymes have more significant effects on cell death than proteins hydrolyzed by other enzymes. In addition, the colostrum protein hydrolysates from skimmed milk were better than those from caseins and whey in inhibiting U937 cell growth.