lupus nephritis accounts for the most morbidity and mortality in patients with SLE. Glucocorticoids combined with cyclophosphamide (CYC) are effective for the treatment of patients with proliferative lupus nephritis and have been the immunosuppressive regimen of choice for many years. However, some patients do not respond well to the regimen, and adverse effects of cyclophosphamide limit its use in certain patients. Leflunomide is a novel immunosuppressive agent currently used in the treatment of rheumatoid arthritis.There were a few pilot observational studies and reports suggesting leflunomide was also safe, well-tolerated and may be effective in SLE patients without important organ involvement. It has not been shown if leflunomide can be used in the treatment of patients with lupus nephritis. We therefore undertook a multi-center, controlled study to investigate the efficacy and safety profile of leflunomide compared with cyclophosphamide in the treatment of patients with biopsy proven proliferative lupus nephritis.