The effect was clarified in humans of protein intake on the mineral balance of calcium (Ca), magnesium (Mg) and phosphorus (P) after consuming an experimental diet without supplementation. The relationship between the protein intake calculated from the diet menu and data from mineral balance studies on 104 Japanese students was analyzed. The protein intake ranged between 64 and 136g/d, or 0.97 and 2.80g/kg of body weight (BW)/d. The respective intake of Ca, Mg and P was in the range of 294-1, 131, 154-379, and 807-2, 217mg/d, or 4.83-23.58, 2.44-7.83 and 13.46-45.69mg/kg of BW/d. The protein intake was well correlated with the mineral intake of Ca, Mg and P, and with the apparent absorption and urine excretion of the minerals. However, the protein intake was not correlated with the balance of these three minerals, while the intake of Ca and P was significantly correlated with the balance of the respective minerals. The protein intake seemed to have no effect on the balance of Ca, Mg and P for the experimental diet without supplementation or when using the data from mineral balance studies.