Ulcerative colitis (UC) is a chronic, relapsing, and incurable inflammatory disease of the large intestine. The hallmark clinical symptoms include bloody diarrhea associated with rectal urgency and tenesmus.. This study will assess how effective upadacitinib is in treating UC within a Chinese population. Upadacitinib is an approved drug for treating UC. Approximately 80 adult participants, who have been prescribed upadacitinib for UC by their physician in accordance with local label, will be enrolled in China. Upadacitinib will be administered in accordance with the terms of the local marketing authorization, and treatment of participants will be determined solely by the investigator. Participants in the study will be followed for up to 1 year. There will be no additional burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic and only data which are routinely collected during a regular visit will be utilized for this study.