Pseudopolyps represent discrete areas of mucosal inflammation and regeneration that are seen in a variety of inflammatory bowel disease including ulcerative colitis and Crohn's disease. These polyps are typically short, measuring less than 1.5 cm in height. Rarely, localized giant pseudopolyposis can occur, i.e., a collection of larger inflammatory pseudopolyps giving rise to a mass lesion within the colon. The most serious problem concerned with pseudopolyposis is a confusion with carcinoma. We experienced a case of localized giant pseudopolyposis causing partial large bowel obstruction. Right hemicolectomy was done for a preoperative diagnosis of ascending colon carcinoma. The resected specimen contained a circumferential lesion, which was composed of numerous interconnecting cylindrical villi, measuring 12 cm in length and 3 cm in height. Microscopically, these polypoid lesions were inflammatory pseudopolyps. Several deep fissure-like ulcerations were noted with multifocal microabscess, lymphoid hyperplasia and an area of noncaseating granuloma.