To study the effect of Yiqi Jiedu formula on the serum levels of TNF-α during the acute and chronic phase in rats with ulcerative colitis(UC). Methods: Using immune and chemical methods (rabbit colonic mucosa sensitized and TNBS/50% alcohol coloystered) to acquire UC models, then randomly divide one hundred rat models into four groups: normol group(30), model group(30), Yiqi Jiedu formula group(20) and mesalazine group(20). To observe the curative effect and test the serum level of TNF-α during the acute and chronic phase of UC. Results: After acquired UC rat model, the serum level of TNF-α in model group is significantly higher than the normal group(P<0.01). Compared with the first day of modeling, the level in the acute and chronic phase is lower in the UC rat model(P<0.05), but it is significantly higher than that of the normal group(P<0.01). In the acute phase, the serum TNF-α levels of Yiqi Jiedu formula group and mesalazine group are lower than the model group(P<0.05), but is higher than that of the normal group(P<0.05, P<0.01). Moreover, the level of the mesalazine group is lower than that of the Yiqi Jiedu formula group(P<0.05). In the chronic phase, the serum TNF-α levels of Yiqi Jiedu formula group and mesalazine group kept falling. The difference of both groups between the normal group decreased(P<0.05), while the level are still significantly higher than the normal group(P<0.01). However, the gap between the two groups are narrow.The decrease degree of Yiqi Jiedu formula group is more obvious in acute phase than chronic phase(P<0.05). In regards to the decrease gap between the acute phase and chronic phase, the Yiqi Jiedu formula group is significantly greater than that of the mesalazine group. Conclusion: The overall effect of Yiqi Jiedu formula is similar to mesalazine. Mesalazine can play a well role on controlling inflammation, so it can be used in acute phase. While in the respect of accelerating UC cicatrization and repairing mucosa hyperplasia, Yiqi Jiedu formula is equal to masalazine and it out performed mesalazine in anti-inflammation and strengthening immunity.