This study is to investigate the effects of paeoniflorin (Pae) on the levels of related serum antibodies and cAMP of splenocytes in rats with adjuvant arthritis. Complete Freund's adjuvant was used to induce AA in rats. The level of circulating immune complexes in serum was determined by PEG6000 assay, and the levels of anti-C II antibody and anti-TB antibody in serum were measured by enzyme-linked immunosorbent assay (ELISA), the level of cAMP in splenocytes was measured by radioimmunoassay, separately. Pae (25, 50, and 100 mg x kg(-1)) and GTW (40 mg x kg(-1)) were given by intragastric administration for 7 days from the 17th day after immunization. Pae (50 and 100 mg x kg(-1)) reduced the levels of circulating immune complexes, anti-C II antibody and anti-TB antibody in serum in rats with adjuvant arthritis. The inhibition ratios of Pae groups to AA model group were dosage-dependent; Pae (12.5, 62.5, and 312.5 mg x L(-1)) decreased the elevated levels of cAMP in splenocytes in vitro. Pae (ig) decreased the levels of related serum antibodies and elevated the level of cAMP in rats with adjuvant arthritis.