1. Completion of induction study HMPL-004-03 or HMPL-004-05 and achieving clinical remission or response with no disruption of study treatment in the transition to HMPL-004-04, or, for the open label induction phase of the study: have active mild to moderate Ulcerative Colitis defined by a modified Mayo Score of 4 to 10 and with endoscopy score activity of 2-3 points confirmed by a full colonoscopy within 2 weeks prior to study.