Abstract: High magnesium intakes are known to inhibit the development of nephrocalcinosis in female rats but there was no information on the dose-response relationship and the underlying mechanism. In an attempt to collect the lacking information, female rats were fed diets containing 0.02-0.24% magnesium as the only variable. Increasing dietary magnesium concentrations were found to reduce nephrocalcinosis in a dose-dependent fashion. The lowest dietary magnesium level produced a kidney calcium concentration of 10.6% in the dry matter whereas the highest magnesium intake reduced kidney calcium to 0.2%. Increasing dietary magnesium concentrations produced increasing urinary magnesium concentrations in combination with decreasing phosphorus concentrations. It is suggested that the magnesium-induced inhibition of nephrocalcinosis is caused by a decrease in urinary phosphorus and increase in urinary magnesium.