Background/aims: To assess intestinal inflammation, simple, inexpensive and objective tools are desirable in inflammatory bowel disease. This study aimed to evaluate fecal calprotectin as a marker of active disease in ulcerative colitis. Materials and Methods: Sixty patients with a diagnosis of ulcerative colitis and 20 controls were recruited into the study. The disease activity of ulcerative colitis was determined by modified Truelove-Witts criteria and Rachmilewitz endoscopic index. The enzyme-linked immunosorbent assay was used to measure the concentrations of fecal calprotectin. C-reactive protein, erythrocyte sedimentation rate and hemogram were also measured, and inflammatory markers were compared with fecal calprotectin in determining disease activity. Results: Fecal calprotectin concentration in the patients with active ulcerative colitis (n=30) was significantly higher than that in the inactive ulcerative colitis group (n=30) and in the controls (n=20) (95% confidence interval: 232.5 (0.75-625) vs 11.7 (0.2-625), 7.5 (0.5-512) mg/L, p<0.001). There was no significant difference between the patients with inactive ulcerative colitis and controls (p>0.05). The calprotectin concentration was greater in the patients with a more severe clinical index, higher endoscopic activity (>4), elevated C-reactive protein, leukocytosis, and extensive colitis (p<0.05). The areas under the curve of the receiver operating characteristics were 0.817, 0.809, 0.532, and 0.507 for C-reactive protein, fecal calprotectin, leukocyte count, and erythrocyte sedimentation rate, respectively. There was a significant correlation between the fecal calprotectin concentration and the endoscopic activity in ulcerative colitis (r = 0.548, p<0.001). Conclusions: Fecal calprotectin is a useful marker in the diagnosis of active disease and evaluation of clinical and endoscopic activity in ulcerative colitis.