We report the case of a 15-year-old Japanese female with severe mesangial proliferative IgA glomerulonephritis who showed a dramatic response to cocktail therapy for nephrotic syndrome. She had suddenly developed massive proteinuria and microscopic hematuria. The first renal biopsy at one month after onset revealed severe mesangial hypercellularity and podocytic detachment from the glomerular basement membrane (GBM). The cocktail therapy resulted in a decrease of proteinuria clinically, and a second biopsy demonstrated repair of the podocytic detachment. We suggest that the massive proteinuria in this case was due to destruction of the size barrier by detachment of podocytes from the GBM, and the repair of the podocytic covering on the GBM was accelerated by the cocktail therapy.