SASP, 5-ASA, 4ASA are effectivedrugs for ulcerative colitis. They contain the same structure, but their action modes are different. The precise mechanism of salicylates are unclear. SASP,5-ASA inhibit inflammatory mediators, but 4ASA has no effect on PG or LT. 5-ASA has a strong force to scavenge the reactive oxygen metabolites. 4-ASA is weak in this aspect. The salicylates influence the function of several cy-tokines at different degree, such as IL-1, IL-6, IL-2, INF-a, TNF-r, GM-CSF, etc, probably bypreventing the binding of cytokine and receptor, or decreasing some cytokine synthesis and liberation. SASP inhibits neutrophilial cell degrandulation, releases lysosome and other enzymes, and changes the activity of lymphacyte. The salicylates also effect nitric oxide synthesis,adhesion molecules and the intestine permeability.