Xanthogranulomatous pyelonephritis is a rare disease of the kidney. The pre-operative diagnosis of this disease is usually very difficult. Recently, echo-guided aspiration biopsy has been suggested for the differential diagnosis of the renal mass. We experienced a case of xanthogranulomatous pyelonephritis and performed echo-guided aspiration biopsy. A 57-year-old female was admitted to our hospital with complaints of upper abdominal pain and right lumbago. Judging from the findings obtained by intravenous pyelography, computed tomographic scan, ultrasonography and angiography, the lesion was a right renal inflammatory mass but renal tumor could not be denied. Because clear cell carcinoma was suspected from the results of echo-guided aspiration biopsy, right radical nephrectomy was performed. However, the resected kidney was diagnosed to be xanthogranulomatous pyelonephritis. Post-operative course was uneventful.