We studied whether differences in the quantities of phosphorus （P） and fat in a low-protein diet affect kidney calcification in rats. Four-wk-old, female Fischer rats were fed one of the following diets ad libitum for 40 days. The six experimental diets contained 10% protein, 0.28% P （equivalent to the level of P in the AIN-93G diet）, 0.52% calcium （Ca） and 5, 10 or 20% oil, or 10% protein, 0.4% P （equivalent to the level of P in the AIN-76 diet）, 0.52% Ca and 5, 10 or 20% oil. The standard diet group was fed a diet containing 0.40% P, 0.52% Ca and 5% oil with 20% protein. After feeding the rats the respective diet for 40 days, they were anesthetized with Nembutal. Among rats that were fed a low-protein （10% protein） diet, reducing the quantity of P in the low-protein diet from 0.40% to 0.28% reduced kidney calcification. In addition, increasing the intake of fat aggravated kidney calcification. Thus, it was revealed that calcification of kidneys that occurred in rats fed the AIN-76 purified diet （AIN-76） was affected by the quantities of P and fat in the feed.