A Study to Evaluate the Safety and Efficacy of AJM300 in Participants With Active Ulcerative Colitis

Major Inclusion Criteria:

• Participants diagnosed with ulcerative colitis.
• Participants with moderate ulcerative colitis who satisfy all of the following criteria at Day of enrollment.

• Mayo Clinic scores of 6-10 .
• Endoscopic subscore greater than or equal to (>=) 2.
• Rectal bleeding subscore >=1.
• Participants with inadequate response or intolerant to oral 5-ASA
• Participants who are capable of providing written informed consent

Major Exclusion Criteria:

• Participants with extensive detachment of mucosa or deep ulcer.
• Participants with oral corticosteroid dependency.
• Participants with a complication of marked reduction of immune function.
• Participants who were clinically suspected to have a complication of infectious enteritis.
• Participants with a history or complication of serious infection within 1 year prior to the day of enrollment.
• Participants with central nervous system (CNS) neurological symptoms.
• Participants with the following criteria:

• Serious heart disease
• Renal impairment
• Hepatic impairment
• Participants with a history of serious drug induced allergy with unknown cause.
• Participants with malignant tumor or those whose treatments were completed in less than 5 years.
• Participants with apparent psychological signs.
• Pregnant women, nursing women, women with suspected pregnancy, women who wish to become pregnant during the period from informed consent through to the end of observation/examination at Week 8, and women who do not consent to the use of appropriate birth control methods.
• Participants who are definitely eligible for surgical intervention such as large bowel perforation, major bleeding, and toxic megacolon syndrome, etc.
• Participants who are participants of another clinical study including follow-up observation at the time of informed consent.
• Participants who received another investigational drug within 12 weeks prior to the examinations/observation defined by the protocol.
• Participants who received investigational drugs in the study of AJM300.
• Participants determined to be ineligible for participation in this study by the investigator or sub-investigator.