Calcium and magnesium in polished rice, polished barley, what flour, and corn which were used for Yakju fermentation were determined by atomic absorption spectrophotometry and their quantitative changes in the filtrates of mashes were checked at 24 hours intervals dueing the whole brewing period. The results obtained were as follows. 1) Mineral contens of raw materials(mg% of each anhydrous materials). Ca : polished rice 8.21, polished barley 26.11, wheat flour 66.10, corn 86.63 2) Mineral contents of kojies made from raw materials (mg %of each anhydrous materials). Ca : rice koji 26.36, barley koji 97.61, what flour koji 87.69, corn koji 16.13, seeding koji 28.76 Mg: rice koji 29.29, barley koji 39.84, what flour koji 244.50, corn koji 102.64, seeding koji 143.79 3) Quantitative changes of minerals in the fitrates of mashes. Calcium contents in the filtrates of mashes were increased gradually after mashing in the first stage but unchanged till the mashes were ripened after mashing in the second stage. On the other hand, magnesium cotents were decreased gradually after increase in the the other hand, magnesium contens were decreased gradually after increase in the first stage but showed a tendency to increase gradually in the second stage. 4)Mineral contents of Yakjues produced, marketing Yakju, and natural water for brewing (g/ml). Ca : rice Yakju 72.38, barley Yakju 84.08, what flour Yakju 105.32, corn Yakju 71.26, marketing Yakju 71.50, natural water for brewing 51.25 Mg :rice Yakju 93.67, barley Yakju 62.39, wheat flour Yakju 273.34, corn Yakju 321,60, marketing Yakju 90.00, natrual water for brewing 20.00 5) Mineral contents of Yakju residues (mg% of each anhydrous matrials). Ca : rice Yakju residues 209.70, barley Yakju residues 62.83, what flour Yakju residues 133.92, corn Yakju residues 60.64 Mg : rice Yakju residues 15.62, barley Yakju residuet 13.22, wheat flour Yakju residues 59.10, corn Yakju residues 67.38