Megalocytic interstitial nephritis is a rare form of kidney disease caused by chronic inflammation. We report a case of megalocytic interstitial nephritis occurring in a 45-yrold woman who presented with oliguric acute kidney injury and acute pyelonephritis accompanied by Escherichia coli bacteremia. Her renal function was not recovered despite adequate duration of susceptible antibiotic treatment, accompanied by negative conversion of bacteremia and bacteriuria. Kidney biopsy revealed an infiltration of numerous histiocytes without Michaelis-Gutmann bodies. The patient's renal function was markedly improved after short-term treatment with high-dose steroid.