Background: Endoscopic observation is the most effective method for the evaluation of staging in ulcerative colitis (UC). However, in cases with very mild inflammatory activity, histopathological diagnosis may also be required. Unfortunately, biopsy-related accidents are not uncommon. As an alternative, we have used a magnifying colonoscope commonly used for tumor diagnosis to examine in detail the colon mucosa of UC patients in clinical remission, and then compared these findings relative to conventional endoscopy using histopathological diagnosis. Subjects and Methods: Among UC cases examined by colonoscopy between April 2000 and April 2005, 27 cases without hematochezia for at least 1 month were enrolled in this study. Following observations of inflammatory changes using conventional colonoscopy, magnifying observation and biopsies at a total of 144 sites were evaluated. Using histopathological standards, acute-phase inflammation was indicated by the presence of neutrophil infiltration, whereas chronic-phase inflammation was indicated by infiltration of lymphocytes, plasma cells and eosinophils. Results: Indicators of significant inflammation by conventional observation was erosion. Under magnification, inflammation appears as superficial defects in mucosa and small whitish spots. When the presence of infiltrating neutrophils was used as a positive histological marker for inflammation, there was no difference in the accuracy of diagnosis by conventional observation (95.1%) versus magnifying observation (97.2%). In contrast, when lymphocyte infiltration was used as a marker, the accuracy of diagnosis increased significantly (88.2%) using magnifying observation relative to conventional observation (61.1%). Conclusions: Magnifying endoscopy can be used effectively in the evaluation of minute mucosal changes in cases of UC remission.