A glaze containing 8wt% Fe2O3 was fired in various atmospheres with the same firing schedule. The effect of firing atmosphere on the color of the iron glaze was studied with a color analyzer, and by ESR, X-ray diffraction, and EPMA.(1) The glaze fired in oxidizing atmospheres was black irrespective of the firing conditions, but the color of glaze fired in reducing atmospheres varied with the onset temperature of reduction.(2) The color of the glazes which were reduced at 900° or 1000°C was black with red spots. The glazes which were reduced at 1100° and 1200°C were red and black, respectively.(3) The results of ESR, X-ray diffraction and EPMA suggested that the black color of the glaze fired in oxidizing atmospheres was caused by the coexisting Fe3+ and Fe2+ ions. The black and the red colors in the glaze fired in reducing atmospheres were due to aggregated metallic iron and aggregated Hematite, respectively.