Abstract: The study summarizes the clinical experience of Professor Zhu Ying, the inherited instructor of academic experience from the national veteran Chinese medicine experts, in the syndrome differentiation and treatment of ulcerative colitis from the theory of potential toxin. It is believed that the core pathogenesis of ulcerative colitis includes vital qi deficiencies leading to lingering pathogens, and collateral damages caused by the potential toxin. In view of that, we propose the treatment principles of treating and differentiating both syndromes and root causes by stages, controlling the development of existing disease by expelling the potential toxin, as well as preventing the recurrence of the disease by caring the spleen and kidney. Clinically, the treatment is to support healthy energy by fortifying the spleen, supplemented by draining the liver and warming the kidneys. In addition, some therapies such as eliminating wind, purging heat, resolving dampness, dispersing pain, and expelling phlegm are applied to cleanse the potential toxin.