Abstract: In Rheumatoid Arthritis (RA) osteoporosis is secondary. Its cause and its treatment are still controversial. All agents used in post menopausal osteoporosis have been tried for RA osteoporosis. Our work is a prospective open study to demonstrate the efficacy of low dose NF (20 mg daily) in these patients. Sixty two patients with RA and osteoporosis (t score less than 2.5 standard deviation, as defined by WHO) entered the study. BMD was measured by Dual Energy X-Ray Absorptiometry (DEXA) on L1-L4 (lumbar spine) and the femoral neck, before and after one year of treatment. NF was given in a slow release formula (20 mg tablet) once a day with meal. Calcium carbonate (1500 mg calcium element daily) was given as 500 mg tablets with 400 I.U. vitamin D3. Both NF tablets and Calcium D were formulated and manufactured by Darou Pakhsh Pharmaceutical Research Center. Serum calcium, phosphorus, and alkaline phosphatase was measured every 3 months with 24 urinary calcium excretion. Results: In 60% of patients (CI=12) both spine and femoral neck responded favorably. In 29% either the spine or the femoral neck responded to the treatment. In 11% (CI=8) both sites lost bone despite the treatment. The mean BMD of the spine increased by 2.6% and the femoral neck by 0.6% annually. In the responder group the mean improvement was 4.3% for the spine (81% of patients) and 4.1% for the femoral neck (68% of patients). Patients in remission responded better to NF than those with active disease. The difference reached statistical significance only for the spine (3.8% increase in the remission group, 1.2% in the active disease group). When compared with Post menopausal women without RA, they responded better to NF than RA patients. The difference was 1% in average, but it did not reach statistical significance. Conclusion: RA patients respond to NF as good as postmenopausal women. Patients in remission responded better than those with active disease. Considering the safety of NF, it must be used not only as a curative treatment but also as a preventive measure in RA patients.