Abstract: The microstructures and nano-mechanical properties of dental dentin and dental enamel were studied by means of OM，SEM，HRTEM and nano indentation equipment. The results show that the dental dentin  consists of dentinal tubules and dentinal matrix，while the dental enamel is built up by enamel prisms and enamel matrix，and there is an obvious interface between dentin and enamel. It is also found that the content of Ca and P in enamel is higher than that in the dentin，while the content of carbon in enamel is lower than that in the dentin. A large quantity of hydroxyapatite (HA) crystal is found in enamel  compared with  that in dentin. The nano-hardness and elastic modulus of the enamel are determined to be 4.4 GPa and 81 GPa, respectively，while the nano-hardness and elastic modulus of the dentin are determined to be 1.0 GPa and 26 GPa on the other hand. The higher hardness of enamel is related to  the formation of crystal phase of HA structure，and Ca and P have a great contribution to the formation of this structure.