A 48-year-old man without underlying disease developed mediastinitis and was treated by mediastinal drainage. Methicillin-resistant Staphylococcus aureus (MRSA) was detected in a culture of the abscess material. He was treated with anti-MRSA antibiotics and the MRSA infection improved. Four weeks after the onset of MRSA infection, he developed rapidly progressive glomerulonephritis (RPGN) with nephrotic syndrome (NS). A renal biopsy showed endocapillary proliferative glomerulonephritis with IgA-predominant glomerular deposition. These clinicopathological findings were consistent with those in glomerulonephritis following MRSA infection (post-MRSA infection glomerulonephritis). The level of serum creatinine increased to 6.3 mg/dl, 7 weeks after the onset of RPGN. At that time, the eradication of MRSA infection was considered. He was given middle-dose steroid therapy. Thereafter, his RPGN with NS improved. MRSA infection did not recur. If the disease activity of post-MRSA infection glomerulonephritis persists after the disappearance of MRSA infection, the application of immunosuppressive therapy with steroids may be useful.