Glomerulonephritis and renal failure represent one of the most life-threatening manifestations of systemic lupus erythematosus (SLE). Although immunosuppressive therapy is often effective for the treatment of acute lupus nephritis, a significant proportion of patients show persistent proteinuria after resolution of the acute nephritic process, and develop progressive renal failure. There is preliminary evidence that calcitriol and other vitamin D analogs can reduce proteinuria in patients with chronic kidney diseases. The investigators plan to conduct a randomized control study to evaluate the safety and efficacy of calcitriol in the treatment of SLE patients with persistent proteinuria. Sixty patients with clinically quiescent SLE and persistent proteinuria despite conventional therapy will be recruited. They will be treated with calcitriol for 48 weeks. Proteinuria, renal function, lupus disease activity, serum and urinary inflammatory markers will be monitored. This study will explore the potential anti-proteinuric and immunomodulating effects of calcitriol in the treatment of SLE, which is a common and life threatening disease in young adults.