This research investigates the effects of bovine colostrums and their protein hydrolysates on human mononuclear cell (MNC) growth, on the secretion of cytokines (interleukin-1β, interferon-γ and tumor necrosis factor-α) as well as nitric oxide, and on the growth inhibition of human leukemic U937 cells. The results indicate that the colostrum hydrolysates obtained by porcine small-intestinal enzymes (PIS) exhibit more significant inhibitory effect on U937 cell growth than do the caseins (PIC) and the whey (PIW) hydrolysates (PIS 57.45%, PIC 42.58% and PIW 48.47% at 1,000 µg/mL). The greatest growth index of MNC, up to 1.43, was achieved by a treatment of PIS at 300 µg/mL for 3 days. The cytokines (IL-1β, TNF-α and IFN-γ) secretion of MNC by a treatment of PIS for 3 days (at 800 µg/mL) was 4,443.35, 325.04 and 4,649.67 pg/mL, respectively. The results suggest that bovine colostrum protein hydrolysates may be utilized in functional food.