Abstract: Objective：To detect the levels of serum decoy receptor 3 (DcR3), IFN-γ, TNF-α and IL-4 in the patients with ankylosing spondylitis (AS), and explore their clinical significance. Methods：The levels of DcR3, IFN-γ, TNF-α and IL-4 in serum samples from 66 patients with AS and 48 healthy controls were determined by enzyme linked immunosorbent assay (ELISA). Then, the correlations of serum DcR3 level with clinical stage of AS and AS associated laboratory markers were analyzed. Results：The levels of serum DcR3, TNF-α and IL-4 in AS patients were significantly higher than that in healthy controls (P<0.05 or P<0.01), and the serum DcR3 level in the active AS patients was significantly higher than that in the inactive AS patients (P<0.05). The ratio of serum IFN-γ/IL-4 (TH1/TH2) in AS patients was significantly lower than that in healthy controls (P<0.01). The serum DcR3 level was positively related to serum IL-4, TNF-α and CRP levels, ESR and BASDAI score (r=0.45, 0.31, 0.38, 0.41 and 0.65, P<0.01) respectively, and negatively related to the IFN-γ/IL-4 ratio (r=-0.38, P<0.01), but unrelated to serum IFN-γ level and PLT (r=-0.12 and 0.23, P>0.05). Conclusion：The serum DcR3 level in AS patients increased significantly, indicating that both TH1 and TH2 cytokines may increase in AS patients, and that the effect of TH2 response is higher than that of TH1 response.