A multi-center, randomized, controlled clinical trial to evaluate the short-term and long-term efficacy and safety of mycophenolate mofetil (MMF) in reducing proteinuria and preserving renal function in patients with IgAN who have pre-treated (and continue to be treated) with angiotensin II receptor blockers (ARB), compared to the corticosteroids.

There are four phases of study for each subject. Phase 1 the screening phase. During this phase each potential subject will be evaluated to determine if he/she is eligible for the study.

Phase 2 the ARB lead-in phase will last for three months. Phase 3 the intervention phase. Each subject will be randomly received 12 months treatment with the study drugs (MMF, prednisone or MMF plus prednisone) Phase 4 following-up phase. All the patients will be followed by 3 years after study drug stopped.

Inclusion Criteria:

• Willingness to sign an informed consent
• Age:14~60 years, regardless of gender
• Clinical evaluation and renal biopsy diagnostic for IgAN, excluded secondary IgAN. Renal histological criteria should be defined by Lee's glomerular grading system.
• 1 g/day <= proteinuria < 3.5 g/day, or UPr/Cr ratio ≥ 0.6 (male) or ≥ 0.8 (female) when taking ARB
• eGFR ≥ 40 mL/min/1.73 m2

Exclusion Criteria:

• Inability or unwillingness to sign the informed consent
• Inability or unwillingness to meet the scheme demands raised by the investigators
• Rapidly progressive nephritic syndrome and acute renal failure, including rapidly progressive IgAN ( IgAN with rapid decline in renal function characterized histologically by necrotizing vasculitis and crescent formation≥30%) necessitating the use of other immunosuppressive agents.
• Secondary IgAN such as systemic lupus erythematosus, Henoch-Schonlein purpuric nephritis and hepatitis B -associated nephritis
• est GFR < 40 mL/min/1.73m2
• Malignant hypertension that is difficult to be controlled by oral drugs
• Cirrhosis, chronic active liver disease.
• History of significant gastrointestinal disorders (e.g. severe chronic diarrhea or active peptic ulcer disease.)
• Any Active systemic infection or history of serious infection within one month of entry or known infection with HIV, hepatitis B, or hepatitis C.
• Other major organ system disease (e.g. serious cardiovascular diseases including congestive heart failure , chronic obstructive pulmonary disease, asthma requiring oral steroid treatment or central nervous system diseases)
• Malignant tumors (except fully cured basal cell carcinoma)
• Absolute neutrophil count < 1500／mm3, absolute platelet count <75000／mm3 or hematocrit (Hct) <28% (anemic subjects may be reevaluated after the anemia has been treated.)
• Known allergy, contraindication or intolerance to the MMF, corticosteroids or ACEI/ARB.
• Pregnancy or breast feeding at the time of entry or unwillingness to comply with measures for contraception
• Current exposure to MMF or azathioprine. In case of current treatment with oral steroid or ACEI/ARB, entry is permitted after corticosteroids or ACEI/ARB are stopped for 2 weeks.
• Current or recent (within 30 days) exposure to any other investigational drugs