A 51-year-old man with chronic myeloid leukemia undergoing treatment with dasatinib received colonoscopy for a positive fecal occult blood test. Colonoscopy revealed more than 100 erythematous, multilobulated polyps with mucoid discharge. Endoscopic mucosal resection was performed for diagnosis, and the histological analysis of polyps showed hyperplastic glands and proliferative smooth muscle cells. Our findings suggested that the polyposis was caused by inflammation triggered due to the adverse effects associated with dasatinib. The patient discontinued dasatinib;the follow-up colonoscopy performed four months later revealed significantly improved polypoid lesions in the colon. The erythematous heads of the polyps and mucoid discharge disappeared. The cessation of dasatinib seemed to contribute to the improvement of inflammatory reactive polyposis;therefore, we inferred that the polyposis was caused by dasatinib in the present case.