There are few reports on the pharmacokinetics of Qing Dai. Because Qing Dai appears in the stool without significant digestion, the mucosal healing effect could be associated with the ability of Qing Dai to provide a protective coating to the injured mucosa. Qing Dai has been reported to have anti-inflammatory effects on human neutrophils based on its ability to suppress superoxide generation[11]. The same authors reported efficacy of Qing Dai in patients with recalcitrant psoriasis in a randomized study[12]. Indirubin, a constituent of Qing Dai, has been reported to produce anti-inflammatory effects by suppressing interferon-α, interleukin-6[13], and nuclear factor κB (NF-κB) production[14]. Xilei-san was also reported to decrease the expression of toll-like receptor 4, NF-κB, and tumor necrosis factor-α in mice with oxazolone-induced colitis[15]. Interestingly, cytapheresis, which has been used in patients with active UC as a highly effective therapeutic, possesses a similar mechanism of action by decreasing reactive oxygen-producing neutrophils and interleukin-6 secretion[16]. In the present investigation, although we observed a strong hydroxyl radical scavenging effect in Qing Dai, further studies are warranted to fully understand the mechanisms of action in UC patients.