We evaluated the association between endoscopic scores of colonic inflammation and fecal calprotectin (FC), fecal immunochemical occult blood test (FIT), and C-reactive protein (CRP) in patients with ulcerative colitis (UC). Endoscopic scores reflecting the most severe lesion [maximum Mayo Endoscopic Subscore (M-MES) and Ulcerative Colitis Endoscopic Index of Severity (UCEIS)] and those reflecting the inflammation of the entire colon [sum of MES (S-MES) and Ulcerative Colitis Colonoscopic Index of Severity (UCCIS)] were evaluated. FC, FIT, and CRP were measured, and their association with the four endoscopic scores was evaluated. Endoscopic scores of 78 complete colonoscopies (66 UC patients) were evaluated using the three biomarkers. FC and CRP tended to correlate more strongly with S-MES and UCCIS than with M-MES and UCEIS. In the M-MES 0, 1 group, compared to CRP, FC and FIT showed stronger correlations with S-MES and UCCIS. Conversely, in the M-MES 2, 3 group, only CRP was significantly correlated with each descriptor. CRP more strongly reflects colon-wide mucosal inflammation than FC and allows reliable assessment of inflammation throughout the colon in active UC.