Abstract: Objective: To investigate the significance of HLA-B27 in the progression and prognosis of patients with undifferentiated spondyloarthropathy (uSpA).Methods: The clinical and laboratory manifestations of 78 uSpA patients with positive HLA-B27 were analyzed and compared with those of 42 patients wit negative HLA-B27.Some of the patients were followed up for 3 years to observe the changes of pathogenetic condition.Results: The HLA-B27 (+) patients had an earlier onset of disease (P<0.05),and more HLA-B27 (+) patients developed general symptoms including fever,weight loss and languor (P<0.05).In the laboratory examination,the erythrocyte sedimentation rates of HLA-B27 (+)group were also increased (P<0.05).There was significant difference in X-ray manifestations between the two groups (P<0.05).One year later,more patients in HLA-B27 (+)group developed ankylosing spondylitis (AS) (P<0.05).Conclusions: HLA-B27 (+) uSpA patients have severer symptoms and a higher rate of developing AS than HLA-B27 (-) patients.HLA-B27 plays an important role in the pathogenesis of uSpA.