We report a case of recurrent IgA nephropathy following renal transplantation under tacrolimus (FK506). A 23-year-old female who had been diagnosed with IgA nephropathy was transplanted from her HLA two-mismatched mother under tacrolimus, prednisolone and azathioprine. Two years after transplantation, suddenly she noticed macroscopic hematuria. At that time, functional renal deterioration (serum creatinine: 2.3 mg/dl) and mild proteinuria were observed. Allograft biopsy disclosed acute cellular rejection. She was administered a bolus injection of methylprednisolone, 15-deoxyspergualin and anti-lymphocyte globulin. However, the response to the treatment was poor. A transplant biopsy revealed focal segmental glomerulosclerosis by PAS staining and granular IgA and C3 deposits on immunofluorescence examination. There was no sign of acute rejection and toxicity by tacrolimus. We diagnosed recurrent IgA nephropathy. At the present time, she has normal urinalysis and renal function is stable (serum creatinine: 1.9 mg/dl). No proteinuria was observed after total dosage of immunosuppressants was increased. Although recurrence of IgA nephropathy in renal allograft is frequent, allograft dysfunction is rare. However, IgA nephropathy has several types with different prognosis. For functional renal deterioration after renal transplantation, we should consider not only an acute rejection or the toxicity of immunosuppressants but also recurrent nephropathy.