INTRODUCTION: Dental caries in enamel is unique amongst diseases as enamel is both acellular and avascular. Thus, in contrast to other tissues, enamel cannot heal itself by a cellular repair mechanism. Nonetheless, it is now well established that the formation of incipient enamel caries is a reversible process where periods of progression alternates with periods of remineralization. OBJECTIVES: The purpose of this study was to compare the effect of Nano-hydroxyapatite paste and casein phosphopeptide-amorphous calcium phosphate fluoride paste remineralizing capacity on initial enamel carious lesions of young permanent teeth. MATERIALS AND METHODS: Sixty extracted young permanent teeth with a standardized window on enamel were immersed in a demineralizing solution for 48 hours to produce subsurface enamel lesions. They were divided into three groups according to remineralizing agents (N=20): group I: Nano-hydroxyapatite paste; group II: casein phosphopeptide-amorphous calcium phosphate fluoride paste; and group III: control (untreated). The enamel surface microhardness (SMH) was measured at baseline, after incipient enamel lesion formation and after treatment. RESULTS: The mean surface microhardness (201.46) was found to be higher in teeth treated with Nano-hydroxyapatite paste than mean surface microhardness (195.61) in those treated with casein phosphopeptide-amorphous calcium phosphate fluoride paste. However, this difference was not statistically significant P=0.26. CONCLUSIONS: Both Nano-hydroxyapatite paste and casein phosphopeptide-amorphous calcium phosphate fluoride paste were effective for remineralization of early caries-like lesions of young permanent teeth.