Calprotectin is one of the major antimicrobial S100 leucocyte proteins. Serum calprotectin levels are associated with certain inflammatory diseases such as rheumatoid arthritis, systemic lupus erythematosus and inflammatory bowel disease. The aim of this study was to investigate serum and fecal calprotectin levels in patients with ankylosing spondylitis (AS) and show their potential relations to the clinical findings of the disease. Fifty-one patients fulfilling the New York criteria of AS and 43 healthy age- and gender-matched volunteers were included in the study. Physical and locomotor system examinations were performed and history data were obtained for all patients. Disease activity parameters were assessed together with anthropometric parameters. Routine laboratory examinations and genetic testing (HLA-B-27) were performed. Serum calprotectin levels and fecal calprotectin levels were measured by an enzyme-linked immunosorbent assay. The mean age of the patients was 41.5 years, the mean duration of the disease was 8.6 years, and the delay in diagnosis was 4.2 years. Serum calprotectin levels were similar in both AS patients and in the control group (p=0.233). Serum calprotectin level was correlated with Bath AS disease activity index (BASDAI) and Bath AS functional index (BASFI) (p=0.001, p=0.002, respectively). A higher level of fecal calprotectin was detected in AS patients when compared with the control group. A statistically significant correlation between fecal calprotectin level and BASDAI, BASFI, C-reactive protein and Erythrocyte sedimentation rate were detected (p=0.002, p=0.005, p=0.001, p=0.002, respectively). The results indicated that fecal calprotectin levels were associated with AS disease findings and activity parameters. Calprotectin is a vital disease activity biomarker for AS and may have an important role in the pathogenesis of the disease. Multi-centered prospective studies are needed in order to provide further insight.