Some physico‐chemical properties of the enamel of deciduous and permanent (young and old) teeth were investigated and compared using x‐ray diffraction, infrared absorption spectroscopy, scanning electron microscopy and chemical analyses. Results demonstrated the following: all enamel samples gave x‐ray diffraction patterns of only apatite; all enamel samples gave IR absorption spectra of carbonate‐containing apatite; the α‐axis of deciduous enamel apatite was larger than that of permanent (both young and old) enamel apatite (mean values, deciduous = 9.458 ± 0.003A; permanent =9 443 ± 0.003A); apatite crystallite dimensions increased with age especially along thec‐axis; when compared to permanent, deciduous enamel contained slightly more carbonate, magnesium and HPO42‐; the prism (enamel rods) dimensions were slightly smaller, and the extent of acid‐etching was more extensive in deciduous enamel than in permanent enamel. These observations combined with other factors such as the difference in the orientation of and crystal density in prism rods and the difference in conditions of the oral environment between deciduous and permanent enamel may account for the reported observations of a decrease in caries p