There has been few papers regarding the pathologic changes of kidney induced by contrast media, especially in terms of iodine concentration or osmolarity. In order to evaluate histopathologic changes, a series of rat kidneys, after injection of iodinated contrast media, were examined. A total of 220 rats were divided into two groups: those given Urografin-60% by 6.3ml/Kg(1840mg/6.3ml); those given Urografin-76% by 5ml/Kg(1850/5ml). (the same amount of iodine but at different iodine concentration). The kidneys were removed and microscopically examined on 1, 2, 3, 5, 7, 10th days, 2nd, 3rd, 4th, 6th and 12th weeks after injection of contrast media, respectively. The results were as follows:Renal pathologic changes induced by contrast media were congestion and ectatic change of the interstitial vessels, and epithelial degeneration and necrosis of the collecting ducts. Congestion of interstisial vessels and epithelial degeneration and necrosis of the collecting ducts were severe i the higher iodine concentration Urografin-76% group(2100 Osm/Kg H2O) than the Urografin-60% group(1500 Osm/Kg H2O). And above pathological changes persisted for 12weeks without significant interval changes. The authors conclude that the renal damage induced by ionic contrast media becomes more severe in higher concentrations or osmolarities in spite of the same amount of iodine and that the pathologic changes persisted until 12weeks without improvement.