This study will help to show the efficacy of vitamin D and address the optimal strategy to minimize renal injury in IgAN patients.

Inclusion Criteria:

• Biopsy-proven Ig AN patients aged 20-70 years
• Patients with residual proteinuria > 500 mg/g creatinine despite renin-angiotensin system blockade and adequate blood pressure control for more than 3 months
• Patients who give informed consent, and 4) estimated GFR >= 30 ml/min/1.73 m2.

Exclusion Criteria:

• patients < 20 years or > 70 years
• hypersensitivity to vitamin D analogs
• patients who need urgent dialysis
• hypercalcemia within 3 months (uncorrected serum calcium level > 10.2 mg/dL)
• clinical features of rapidly progressive glomerulonephritis
• life expectancy less than 24 months
• uncontrolled hypertension
• decompensated liver or lung disease
• symptomatic heart failure (NYHA class II-IV or LVEF < 40%)
• estimated GFR < 30 ml/min/1.73 m2.