This study was to explore the immunity-promoting activity of porcine placenta as a potential raw material for functional foods. Porcine placenta was subjected to the analysis for its bioactive substances, and their immunity-promoting activity was determined in mice supplemented with porcine placenta extract (PPE) and freeze-dried porcine placenta powder at high (PPH) and low (PPL) dosage. Results showed that porcine placenta contained placental peptides and 15 free amino acids, and the amounts of estrogen and progesterone in products developed from porcine placenta were within the limit of national standard. Mice model experiment revealed that compared with the control, the PPH treatment significantly improved the spleen index (P < 0.05) by increasing the phagocytic rate of macrophages from 20% to 60% and the conversion rate of T lymphocytes from 8% to 60%. The qPCR analysis disclosed that the porcine placenta powder enhanced mice immunity via promoting the expression of Th1 cytokines of interleukin-2 (IL-2) and IFN-γ, especially the former, by almost 8 times in the spleens of male mice, while inhibited Th2 cytokines of IL-4 and IL-10. This investigation has provided a reference for the development of porcine placenta as a raw material applied in functional foods to improve human immunity.