Idiopathic nephrotic syndrome is generally responsive to steroid therapy, but some patients need other immunosuppressants to reduce steroid dependency. The long-term use should be restricted due to adverse effects of cyclosporine, such as hypertension and nephrotoxicity.

Mycophenolate mofetil for steroid-dependent nephrotic syndrome has been reported to have similar efficacy and fewer undesirable effects to other drugs in mainly observational studies. To determine the efficacy of mycophenolate mofetil in the management of steroid-dependent nephrotic syndrome, the investigators designed this prospective randomized controlled study.

Inclusion Criteria:

• Steroid-dependent patients who had been on calcineurin inhibitors continuously for more than 1 year
• in complete remission

Exclusion Criteria:

• Hereditary or secondary nephrotic syndrome
• Estimated glomerular filtration rate (GFR) < 60 mg/min/1.73 m^2
• Body weight <16 kg
• leukocytopenia (absolute neutrophil count < 2000/mm^3) or anemia(Hct < 25%)
• Severe gastrointestinal disease
• chronic or acute active infection (e.g. hepatitis B,C, herpes, varicella zoster)
• prior live vaccine inoculation within 6 weeks (from the study enrollment)
• GOT/GPT elevation or hyperbilirubinemia
• malignant disease
• Pregnant or Breast feeding
• Previous history of mycophenolate mofetil use
• Participation to other therapeutic trial within recent 3 months
• Deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase