An Early Phase 2 Clinical Study of KSP-0243

Inclusion Criteria: * Patients aged 18 to 74 years old (both inclusive) * Patients who have been given the diagnosis of ulcerative colitis for at least 12 weeks * Patients with an endoscopic view typically seen with ulcerative colitis spreading \> 15 cm from the anal verge * Patients with mild to moderate active ulcerative colitis who meet the certain conditions * Patients who have an inadequate response to a fixed-dose oral 5-ASA formulation (mesalazine or salazosulfapyridine) continued from at least 2 weeks prior to the start of the screening period Exclusion Criteria: * Patients who underwent an enterectomy or are expected to require an enterectomy during the study period (except appendectomy) * Patients who have or suspected to have bacterium- or parasite-induced infectious enteritis (e.g., infection with Clostridium difficile) * Patients with any of the following concomitant illnesses with the severity considered inappropriate as a study patient by the principal investigator or the subinvestigator or medical history thereof: * Hepatic or renal disorders or cardiovascular, endocrine, metabolic, pulmonary, gastrointestinal, neurological, urological, genitourinary, and immune diseases,