AIM To evaluate the efficacy and safety of nimesulide in the treatment of rheumatoid arthritis(RA). METHODS An open and multi centre clinical trial in the whole country was performed to study the efficacy and safety of nimesulide on 646 RA patients. These patients were given orally with nimesulide 100 mg twice a day for 4 weeks, of whom 302 were picked out and given nimesulide for another 4 weeks. RESULTS The total efficacy rates of nimesulide were 84 21% after 4 week treatment and 94 70% after 8 week treatment. In the 646 cases, the incidence of adverse reaction of nimesulide was 17 49% after 4 week treatment. Severe adverse reaction occurred in 2 cases.14 had mild adverse reaction and the rest had slight adverse reation. After 8 weeks, the incidence of adverse reaction in the 302 cases was 18 54%, among including, 7 mild and 47 slight case of adverse reaction. CONCLUSION Nimesulide exhibited remarkable efficacy and safety in the treatment of RA.