Varietal differences in contents and balance of phosphorus, potassium and magnesium in kernels of thirty-six cultivars of eleven cereals (Rice, Wheat, Barley, Two-rowed barley, Corn, Sorghum, Job's tears, Proso millet, Barnyard millet, Foxtail millet and Finger millet) were investigated. The dry-ashed materials of whole kernels of 36 cultivars were analyzed by a colorimetric procedure for P, a flame photometry for K and an atomic absorption spectrometry for Mg. P, K and Mg contents of each cereal were almost equal to those of previous studies. (Table 2). Mg/K chemical equivalent ratio as a predictor of grain quality was examined with the 36 cultivars. Most of the cereals used for human consumption (except wheat, barley and two-rowed barley) marked the ratio within 1.25 to 2.0 approximately. These cereals contain more magnesium than potassium in chemical equivalence. Other cereals used for feed marked comparatively low ratio, i.e. approximately 0.9 to 1.25 (Fig. 1). Further studies will be needed on wheat, barley and two-rowed barley to classify by mineral balance, because these cereals contain more calcium than in others.