In this study, p-coumaric acid was evaluated for its immunomodulatory and anti-inflammatory properties in vivo. The immunomodulatory effect of p-coumaric acid (100 mg/kg body weight) was assessed by evaluating its effect on cell-mediated immune responses (delayed type hypersensitivity reaction), serum immunoglobulin levels, and macrophage phagocytic index in rats. The anti-inflammatory effects of p-coumaric acid (100 mg/kg body weight) were investigated by examining its effect on expression of tumor necrosis factor (TNF-α) in synovial tissue by immunofluorescence confocal microscopy and circulating immune complexes in serum of adjuvant-induced arthritic rats. The increased cell-mediated immune responses and macrophage phagocytic index observed in control rats were significantly reduced (p < 0.05) upon treatment with p-coumaric acid implying its immunosuppressive property, whereas serum immunoglobulin levels were found to be increased in p-coumaric acid treated control rats. p-coumaric acid also showed significant (p < 0.05) anti-inflammatory effects in adjuvant-induced arthritic rats by effecting a decrease in the expression of inflammatory mediator TNF-α and circulating immune complexes. Indomethacin was used as a reference drug for anti-inflammatory studies. Thus, our results show that p-coumaric acid could be considered a potential immunosuppressive agent in treating autoimmune inflammatory diseases like rheumatoid arthritis.