Abstract: [Objective] To clarify the effect of Qingrejiedu Therapy and Yiqijianpi Therapy on serum NO of acute and chronic ulcerative colitis rats, and to provide the basis for syndrome differentiation treatment.[Methods] Serum NO level of ulcerative colitis rats was detected. The curative effects of different treatment were observed to explore the anti-inflammatory and immune mechanisms for the treatment of UC. [Results] serum NO level of the model group was significantly higher than that of normal group (P＜0.01) during acute phase, which was decreased during chronic phase (P＜0.01), but still significantly higher than normal group (P＜0.01). In the acute phase, serum NO level of Qingrejiedu Therapy group was significantly lower than model group (P＜0.01), and had no statistical difference compared with normal group. NO level was higher in Yiqijianpi Therapy group and western medicine group compared with normal group (P＜0.01). In the chronic phase, NO level was lower in Qingrejiedu Therapy group, Yiqijianpi Therapy group and the western medicine group compared with model group (P＜0.05). However, the level of NO was obviously lower in Yiqijianpi Therapy group compared with model group, which was also lower than Qingrejiedu Therapy group or western medicine group (P＜0.01). Yiqijianpi Therapy group had a significantly lower NO level in chronic stage than its acute stage (P＜0.01). [Conclusion] The immune and inflammation injury continues to exist in the whole course of UC, especially in acute stage. Excessive Biao of dampness and stasis is the main pathogenesis for acute phase UC, thus Qingrejiedu Therapy can play a better anti-inflammatory effect and achieve significant results. In chronic phase, the main pathogenesis is the weakness of vital qi, thus Yiqijianpi Therapy can improve the immunity to promote immune damage and achieve better therapeutic effect. This provides the objective basis for the syndrome differentiation and treatment of UC.