Our aim in this study was to investigate serum hyaluronic acid (HA) levels and the relationship between clinical parameters in ankylosing spondylitis (AS). Approximately 30 patients with AS and 30 healthy individuals were recruited in this study consecutively. Cross-sectional study was planned, and demographic, clinical, functional, radiological, and laboratory data of patients were evaluated. Disease activity, functional status, and quality of life were assessed, respectively, with Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), and Short-Form 36 (SF-36). Mander Enthesis Index (MEI) was used for evaluation of enthesis involvement. We examined serum concentrations of HA (ng/ml) in patients with AS and controls. The mean ages of patients and control group were 38.3 (SD=10.8) and 42.7 (SD=10.6) years, respectively. The mean of serum HA levels in AS patients was 40.4 (SD=34.8) ng/ml and in controls was 24.9 (SD=20.2). There was significant difference of HA levels between two groups (p=0.04). Furthermore, there was a significant correlation between HA level and distance of hand-floor (r=0.444, p=0.014), modified lumbar Schober's (r= -0.413, p=0.023), distance of chin to chest (r=0.436, p=0.016), right sacroiliit grade (r=0.601, p<0.001), left sacroiliit grade (r=0.610, p<0.001), C reactive protein level (r=0.404, p=0.027), albumin (r= -0.464, p=0.010), C3 (p=0.449, p=0.013), and IgA levels (r=0.369, p=0.045). However, there was no significant correlation between HA levels with MEI, BASFI, BASDAI, and SF-36 (p >or= 0.05). Serum HA level was significantly higher in AS patients than controls. However, there was no significant correlation between serum HA level and disease-specific measures as BASFI and BASDAI; it had significant relation with spinal mobility limitation, sacroiliitis, and laboratory parameters related with acute inflammation. The serum HA level may be a potential biomarker of axial inflammation and disease severity in AS.