In this study, the unaffected, affected and heavily affected teeth were studied by using X-Ray diffraction method. The D-values, which are related to the crystallite size of the apatite crystals, were calculated according to the Sherrer equation. The crystallite size of unaffected enamel was found to be 1530.95Å, while the affected enamel was 1490.22Å and the heavily affected enamel was 1484.16Å respectively. This study showed that the unaffected enamel has greater crystallite size as compared to the affected and heavily affected enamel.