Background and study aim: We aimed to evaluate the validity and accuracy of the faecal calprotectin in differentiating patients with IBD from those with IBS and in the assessment of the severity of intestinal mucosal inflammation in patients with ulcerative colitis (UC) which may facilitate in the prognosis and follow. Patients and Methods: We studied 60 Patients who came to endoscopy unit with lower gastroenterological symptoms. Patients with history of infections, malignancy, gastrointestinal surgery, pregnancy, alcohol abuse or taking nonsteroidal anti-inflammatory drugs were excluded from study. All patients subjected to thorough medical history, simple clinical colitis activity index was determined with a score ˃ 4 indicate active UC, complete blood picture, liver, kidney function tests, ESR, CRP, ANCA were done, a stool sample for FC levels determined by a highly sensitive enzymelinked immunosorbent assay and total colonoscopy with histological examination of intestinal mucosa biopsy were done. The patients divided into 2 groups. Group A: patients with UC, group B: patients with manifestation of irritable bowel syndrome as a control group. Results: There was a high significant difference between individuals with no pathological activity and other degree of mucosal inflammation as regard simple clinical colitis activity index, endoscopic appearance and faecal calprotectin (p = 0.000). The sensitivity, specificity, positive predictive value and negative predictive value of faecal calprotectin in diagnosis of UC were 93.5%, 89.7%, 90.6%, and 92.9% respectively. The positive predictive value and negative predictive value of simple clinical colitis activity index for diagnosis of UC were 76.5% and 80.8% respectively. The positive predictive value and negative predictive value of endoscopic appearance for diagnosis of UC were 100%, and 85.3% respectively. There was a high significant difference and positive correlation between faecal calprotectin, score of colonic pathological activity, endoscopic appearance and simple clinical colitis activity index. Conclusion: Faecal calprotectin is highly useful for the diagnosis and disease monitoring of patients with UC as it is easy, non invasive, reliable tool