Objectives: Analysis of the relationship between fecal calprotectin levels and some clinical and diagnostic characteristics in the IBD and IBS groups. Subjects and methods: A total of 52 patients were diagnosed with IBD and IBS treated at Thai Nguyen National Hospital. Methods: cross-sectional descriptive study. Results: The median of fecal Calprotectin concentration in patients with IBS were 25.70 (32.07)µg/g, in patients with IBD, it were 87.00(51.98)µg/g. There is a statistically significant relationship between Calprotectin levels and symptoms of fever, bloody stools, and UC disease activity according to the fully Mayo scale. However, the study results showed that there was not relationship between Calprotectin levels and weight loss, CD disease activity according to the CDAI scale and IBS disease types. The Calprotectin cut-off was 52.25 µg/g that used to differentiate IBD and IBS with sensitivity and specificity of 87.5% and 82.1%, respectively. The area under the curve is 0.920. Conclusions: Fecal calprotectin is an inflammatory marker that correlates with clinical symptoms of the disease, disease activity, and may contribute to distinguishing between IBD and IBS. Keywords: Inflammatory bowel disease, Crohn’s disease, Ulcerative Colitis, Irritable bowel syndrome, Fecal calprotectin