A 44-year-old man was admitted for evaluation of asymptomatic graft dysfunction. An allograft biopsy revealed diffuse interstitial infiltration of lymphocytes (i3) with moderate tubulitis (t3) and SV40-positive renal tubular epithelial cells. The patient was diagnosed with BK virus nephropathy, and immunosuppression was modified with discontinuing mycophenolate and reducing tacrolimus. Leflunomide treatment was also started simultaneously. However, serum creatinine increased to 3.0 mg/dL; therefore, the patient underwent a second allograft biopsy, in which the crescent was no longer evident but tubulitis (t2) and fibrosis (i2) persisted. On day 20, leflunomide was switched to ciprofloxacin due to leukopenia. The serum creatinine increased to 3.3 mg/dL, and the third biopsy showed slightly improved tubulitis and interstitial inflammation. We then administered an intravenous infusion of immunoglobulin. On day 70, the renal function was stable and the BK serum viral load was low, and the patient was discharged. This is a case of severe crescentic BK nephropathy with successful outcome treated with aggressive treatment and this method will be useful in renal transplant patients.