Objective To observe the expression of macrophage migration inhibitory factor (MIF) in colon tissues of rats with 2,4, 6-trinitrobenzene sulfonic acid (TNBS) induced colitis and the relationship between MIF and the severity of the colitis. Methods 24 Spra-gue-Dawley rats were randomly divided into three groups: normal group, model group Ⅰ and model group Ⅱ. Rat colitis model was induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS), and disease activity index (DAI) was calculated every day. The myeloperoxidase (MPO) ac-tivity was detected by biochemistry, the expression of MIF in colon tissue was detected by semi-quantitative reverse transcriptional chain reac-tive (RT-PCR). Results In normal group, DAI, MPO activity and MIF mRNA level were 0.51±0. 28,0. 38±0. 18,0. 11±0. 03, while in model group Ⅰ were 5.04±0.73,1.68±0. 45,0. 65±0.04 and in model group Ⅱ were 8. 13±0.71,2. 70±0. 35,0. 81±0. 05. Com-pared with normal control, the expression of MIF mRNA significantly increased (P<0.05), MPO activity and DAI also significantly in-creased(P<0.05)in model group, especially in model group Ⅱ. Conclusion The expression of MIF increased in experimental colitis, and there was a positive relation between MIF expression and the severity of colitis, which suggested that MIF may be related to the pathogen-esis of TNBS-induced colitis.