Background Observational studies suggest that patients with immunoglobulin A nephropathy (IgAN) with active proliferative lesions show a good response to immunosuppressive treatment. Study Design Multicenter, prospective, randomized, controlled trial. Setting & Participants 176 patients with IgAN with active proliferative lesions (cellular and fibrocellular crescents, endocapillary hypercellularity, or necrosis), proteinuria with protein excretion ≥ 1.0 g/24 h, and estimated glomerular filtration rate > 30 mL/min/1.73 m2. Intervention Mycophenolate mofetil (MMF) group: MMF, 1.5 g/d, for 6 months and prednisone, 0.4 to 0.6 mg/kg/d, for 2 months and then tapered by 20% per month for the next 4 months; prednisone group: prednisone, 0.8 to 1.0 mg/kg/d, for 2 months and then tapered by 20% per month for the next 4 months. All patients were followed up for another 6 months. Outcomes The primary end point was complete remission rate at 6 and 12 months. Results At baseline, median estimated glomerular filtration rates were 90.2 and 94.3 mL/min/1.73 m2 and mean proteinuria was protein excretion of 2.37 and 2.47 g/24 h in the MMF and prednisone groups, respectively. At 6 months, complete remission rates were 37% (32 of 86 patients) and 38% (33 of 88 patients); the between-group difference was not statistically significant ( P = 0.9). At 12 months, complete remission rates were 48% (35 of 73 patients) and 53% (38 of 72 patients) in the MMF and prednisone groups, respectively; the between-group difference was not statistically significant ( P = 0.6). Incidences of Cushing syndrome and newly diagnosed diabetes mellitus were lower in the MMF group than in the prednisone group. Limitations Not all participants were treated with renin-angiotensin system blockers, relatively short follow-up. Conclusions MMF plus prednisone versus full-dose prednisone did not differ in reducing proteinuria, but patients treated with the former had fewer adverse events in patients with IgAN with active proliferative lesions.