Abstract: OBJECTIVE To investigate effects and mechanism of sodium 4-amino salicylic acid colon localization pellet on chronic ulcerative colonitis. METHODS The rat ulcerative colonmitis model was made with TNBS. With 14 days of treatment through the pellets. The pathology of colon, IL-1B, TNF-a, superoxide dismutase (SOD) and malondialdehyde (MDA) were measured in all groups. RESULTS The sodium 4-amino salicylic acid colon localization pellet could alleviate pathologic damage of ulcer ative colonitis; debased IL-1B, TNF-a in serum, myeloperoxidase (MPO) and MDA in colon, increased SOD in colon; better to cure ulcrrative colonitis arosed by chemicals. CONCLUSION The sodium 4-amino salicylic acid colon localization pellet can effectively inhibit the inflammatory infiltration, inhibit IL-1B and TNF-a expression of the proliferation and to reduce free radical damage may be one of the mechanisms play a role.