Renal injury caused by iodinated contrast media has been widely known, but there has been few papers regarding the pathological change. A series of rat kidneys after injection of iodinated contrast media was examined to document pathologicl change. A total of 80 rats was divided into two groups : those given Urografin-60% by 5$mell$/kg ; those given Urografin-76% by 5$mell$/kg. The kidneys were removed out 1, 2, 3, 5, 7, 10, 14 and 21 days after injection of contrast media and microscopically examined. The results were as follows : 1. Pathological changes induced by ionic contrast media were deposition of proteinaceous materials in the proximal convoluted tubules, congestion of interstitial vessels, and vasa rectae, and epithelial degeneration of collecting ducts. There was no detectable pathological changes in the glomerulus, loop of Henle, and distal convoluted tubules. 2. All the pathological changes were severs, as the concentration of contrast media increase. 3. These pathologic hanges appeared 1 day after injection of contrast media and persisted at least 3 weeks without improvement. Author concludes that the renal damage induced by ionic contrast media becomes severe with increase in concentration, and pathologic changes are not influenced with time interval.