The purpose of this study was to investigate the mineralization mechanism in developing enamel using the pH staining technique. Unerupted bovine teeth were used in the experiment. Activity of a proteolytic enzyme against enamel protein obtained from bovine enamel was evaluated. Crystals in developing enamel, which were classified into neutral zones 1 (Nl) and 2 (N2) and acid zones 1 (Al) and 2 (A2), were investigated using infrared spectroscopy, thermal analysis, and power X-ray diffractometry. The proteolytic enzyme showed highest activity at approximately pH6, which was in accordance with the pH in the acidic zone (Al) . Most of the organic components of the enamel decomposed at 580°C except for the carbonate and hydrogen phosphate groups included in the apatite crystals. In the developing enamel, (Ca+Mg) /P molar ratio was lower than that of the stoichometric hydroxyapatite. The replacement of OH and PO4 sites in apatite crystals was higher than that in matured enamel. The a-axis dimension of the apatite crystals in the secretory stage enamel (N1) was found to be greater than that in A2 and matured enamel. These results suggested that enamel mineralization is followed by decarbonation in carbonate apatite.