Objective：To investigate the differential expression of serum soluble TNFrelated apoptosisinducing ligand (sTRAIL) between ankylosing spondylitis (AS) and rheumatoid arthritis patients (RA) and to discuss its clinical significance. Methods: Sixty AS patients, including 38 HLAB27positive ones and 22 HLAB27negative ones, 20 rheumatoid arthritis (RA) patients and 30 healthy individuals were included in the present study. The AS patients were divided into active group and inactive group based on bath ankylosing spondylitis disease activity index (BASDAI). The concentrations of serum sTRAIL were measured by ELISA in all groups. Erythrocyte sedimentation rate (ESR) and Creactive protein (CRP) were detected automatically by ESR automatic analyzer and specific protein analyzer. Results: The serum sTRAIL concentration was significantly higher in AS patients (both HLAB27positive and negative AS patients) than in RA patients and healthy controls (P<0.01); no significant difference was found between HLAB27positive and negative AS patients. Serum sTRAIL concentration was significantly higher in active AS group than in inactive AS group（P<0.01）. Serum sTRAIL and CRP concentrations were correlated with each other in HLAB27positive AS patients（r=0.609，P=0.000）, but not in HLAB27negative ones. Serum sTRAIL concentration was not correlated with ESR in AS patients. Conclusion: Serum sTRAIL is obviously upregulated in AS patients, which is not associated with the status of HLAB27. However, the association between sTRAIL and CRP is influenced by the status of HLAB27.