A 55-year-old woman developed bilateral leg edema in June 2006. Since the edema tended to worsen, she visited our hospital on November 11. Laboratory tests showed a serum albumin level of 2.5 g/dl with 3+ proteinuria, and suggested nephrotic syndrome, which led to her hospitalization on November 14. The findings of discoid erythema, an antinuclear antibody titer of 1: 640, anti-ds DNA antibody titer of 16.8 IU/ml, and ISN/RPS class III (A/C)+V lupus nephritis on kidney biopsy led to the diagnosis of systemic lupus erythematosus. Treatment with prednisolone at 1 mg/kg/day was initiated. Despite an increase in complement levels and decreases in anti-ds DNA antibody titers and immune complexes, proteinuria persisted; therefore, the patient was concomitantly given 125 mg/day of azathioprine, which was discontinued because of the poor improvement of proteinuria and development of myelosuppression, and replaced by 3 mg/day of tacrolimus (Tac), with a consequent marked improvement in proteinuria. We report a patient with refractory proteinuria due to class III/V lupus nephritis who achieved a Tac-induced complete remission.