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In this study, a low molecular-weight (Mw) peptide named NJP (&lt;1 kDa), was purified from a protein hydrolysate of <i>Nibea japonica</i> by ultrafiltration, and its immunomodulatory effect on RAW264.7 cells was evaluated. The lactate dehydrogenase (LDH) and MTT assays were performed to explore the cytotoxicity of NJP. The results showed that NJP promoted cell proliferation and had no significant toxic effects on RAW264.7 cells. Moreover, the cells formed multiple pseudopodia indicating that they were in activated state. Further tests showed that NJP significantly promoted phagocytic capacity, and the secretion of proinflammatory cytokines tumor necrosis factor-&#945; (TNF-&#945;), interleukin-6 (IL-6), and interleukin-1&#946; (IL-1&#946;). It also increased the synthesis of nitric oxide (NO) by upregulating inducible nitric oxide synthase (iNOS) protein level. Flow cytometry revealed that NJP promoted cell cycle progression and increased the percentage of cells in G0/G1 phase. NJP promoted I&#954;B&#945; degradation, p65 and nuclear factor (NF)-&#954;B activation and translocation by up-regulating IKK&#945;/&#946; protein expression. In conclusion, these results indicated that NJP exerts immunomodulatory effects on RAW264.7 cells through the NF-&#954;B signaling pathway. Therefore, NJP can be incorporated in the production of functional foods or nutraceuticals.