Nimesulide is a non_steroid antiinflammatory_drugs which inhibits cyclooxygenase_2 with high selectivity. The efficacy and safety of nimesulide in the treatment of patients with rheumatoid arthritis were evaluated in the study. Rondomized, double blind, controlled and multi centred clinical trial of nimesulide versus naproxen were performed. Sixty patients were given intragastrically with nimesulide 100 mg twice daily for 2 weeks and another sixty one patients were given intragastrically with naproxen 250 mg twice daily for 2 weeks. There were 28 patients treated for 4 weeks in nimesulide group and 29 patients treated for 4 weeks in naproxen group. The total efficacy rates of nimesulide were 53.33%,60.71% after 2,4 weeks treatment respectively. The total efficacy rates of naproxen were 47.54%,55.17% after 2,4 weeks treatment respectively. Nimesulide and naproxen could both improve the symptom and sign of the chronic inflammation. The incidences of adverse effects of nimesulide were 25.00%,25.00% after 2,4 weeks treatment. The incidences of adverse effects of naproxen were 22.95%,27.59% after 2,4 weeks treatment. Their adverse effects were mild moderate in intensity and predominantly gastrointestinal in nature. Nimesulide has a similar efficacy rates with NAP in the treatment of rheumatoid arthritis for 2 and 4 weeks. There are no significant difference between their adverse effects rates.