Background: Inflammatory bowel disease (IBD) is a chronic immune-related condition caused by interactions between genetics, immune dysfunction, gut microbiota changes, and environmental factors, often presenting as persistent or recurring diarrhea. Clinically, it commonly presents with chronic diarrhea and other gastrointestinal symptoms. The global prevalence of IBD is increasing, currently affecting approximately 0.5% of the population, with projections suggesting a rise to nearly 1% by 2030. Fecal calprotectin is a neutrophil-derived S100 calcium-binding protein that is elevated in intestinal mucosal inflammation and serves as a reliable noninvasive biomarker of inflammatory activity. Due to its high stability and close association with intestinal inflammatory activity, fecal calprotectin has been established as a dependable, non-invasive marker for identifying intestinal inflammation. In clinical practice, it is extensively used to distinguish IBD from functional gastrointestinal disorders, especially irritable bowel syndrome, among patients presenting with chronic diarrhea. However, its diagnostic utility in Mongolia remains underexplored, and this study aims to determine its sensitivity and specificity in inflammatory bowel disease and compare its diagnostic performance with other inflammatory markers. Aim: To determine the sensitivity and specificity of fecal calprotectin in inflammatory bowel disease and to compare it with other inflammatory markers. Materials and Methods: A total of 109 participants aged 18-87 years with chronic diarrhea, who attended the gastroenterology outpatient clinics of the Mongolia–Japan Hospital and Intermed Hospital between December 2024 and December 2025 and provided informed consent, were enrolled in this study. Data were collected using structured questionnaires, and laboratory investigations included complete blood count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and measurement of fecal calprotectin levels from stool samples. Based on fecal calprotectin results, selected participants underwent colonoscopic examination as clinically indicated. Results: Among the 109 participants included in the study, 17.4% were diagnosed with inflammatory bowel disease (IBD), with a mean age of 47.41±15.52 years. Fecal calprotectin levels were significantly higher in the IBD group compared to the control group (p<0.001). Fecal calprotectin demonstrated a weak positive correlation with C-reactive protein (CRP) and leukocyte count (p=0.042, p=0.06), while no significant correlation was observed with erythrocyte sedimentation rate (ESR). At a cutoff value of 250 µg/g, fecal calprotectin showed a sensitivity of 94.4%, specificity of 69.2%, positive predictive value (PPV) of 37.8%, and negative predictive value (NPV) of 98.4%. Receiver operating characteristic (ROC) curve analysis identified an optimal cutoff value of approximately 400 µg/g (AUC=0.919, Youden index=0.724), at which the sensitivity remained 94.4% and specificity increased to 78.0%. In contrast, CRP and ESR demonstrated comparatively lower diagnostic performance, with AUC values of 0.640 and 0.644, respectively. Conclusion This study demonstrates that fecal calprotectin has superior diagnostic performance compared to conventional inflammatory markers in differentiating inflammatory bowel disease (IBD). An optimal cutoff value of approximately 400 µg/g yielded the highest sensitivity and specificity. Therefore, fecal calprotectin may serve as a valuable tool in clinical practice for both screening and diagnostic confirmation.