Immunoglobulin A (IgA) nephropathy is the common type of primary glomerulonephritis in the world. A wealth of literature suggests that vitamin D and its analogs have profound effects on immune system function and glomerular mesangial cell proliferation. However, calcitriol, the standard form of vitamin D, carries a substantial risk of hypercalcemia. Recently, paricalcitol (19-nor-1,25-dihydroxyvitamin D2) was approved for the treatment of secondary hyperparathyroidism in chronic renal failure, and the incidence of hypercalcemia is much lower than calcitriol. Therefore, the investigators plan to conduct a randomized cross-over study to evaluate the efficacy of paricalcitol in the treatment of IgA nephropathy. Thirty patients with biopsy-proven IgA nephropathy will be recruited. They will be randomized to paricalcitol for 12 weeks or no treatment, followed by cross over to the other arm after a washout period. Proteinuria, renal function, serum and urinary inflammatory markers will be monitored. This study will explore the potential anti-proteinuric and anti-inflammatory effects of paricalcitol in the treatment of IgA nephropathy, which has no specific treatment at present.