OBJECTIVE To investigate the efficacy and adverse effect of mycophenolate mofetil (MMF) in the treatment of frequently relapsing nephrotic syndrome in children. METHODS The study population consisted of 37 children (24 simple nephrotic syndrome and 13 nephritis-type syndrome) suffering from frequently relapsing nephrotic syndrome. Patients received 20-30 mg/(kg d) of MMF in conjunction with 1 mg/(kg d) prednisone for 3-6 months. RESULTS Out of 24 patients suffered from simple nephrotic syndrome, 17 patients (70.8%) with complete relief, 4 patients (16.7%) with partial relief and 3 patients (12.5%) with non-relief, whereas out of 13 patients suffered from nephritis-type syndrome 6 patients (46.2%) with complete relief, 3 patients (23.1%) with partial relief and 4 patients (30.7%) with non-relief. Eight patients with Minimal Change Disease (MCD) achieved complete relief. Of 23 patients with Mesangial Proliferative Glomerulonephritis (MsPGN) or Membranoproliferative Glomerulonephritis (MPGN), complete relief was observed in 17 patients (73.9%), partial relief in 4 patients (17.4%) and non-relief in 2 patients. CONCLUSION These Results suggest that MMF has better efficacy against simple renal disease than against nephritis-type syndrome, and MMF may be more suitable for the treatment of frequently relapsing nephrotic syndrome characterized by proliferative lesions.