Investigations of the intact dental enamel as well as carious-affected human dental enamel were performed in the work by X-ray diffraction of synchrotron radiation. Caries of enamel is characterized by decrease of crystallinity index and by the absence of the preferable orientation of hydroxyapatite (HAP) crystals within the affected enamel. It means the presence of the destructive processes in the organic matrix of hydroxyapatite crystal.