Objective: In order to learn more side-effects of Mesalazine,one case that Mesalazine indced fever in a patient with Crohn disease(CD) was investigated.Methods:Many clinical case-report about side-effects of Mesalazine were observed by index system.Results:Patient's temperature returned to normal after Mesalazine disused for two days.Conclusion:It's necessary to pay more attention on rare side-effects of Mesalazine,fever,which was reported less in clinic.