Objective: Instant effects of bleaching- including surface morphology and chemical structure alteration-induced tooth sensitivity which is the main deterrent for patients to successfully complete their bleaching treatment. Fluoride, calcium, or amorphous calcium phosphate could be added to bleaching gel to reduce bleaching effects. This study aimed at comparing different protocols of Nano-Hydroxyapatite (as a promising re-mineralizing agent) incorporation with bleaching gel effect on surface and subsurface enamel morphologically and chemically. Methodology: Twenty-eight sound anterior teeth were collected from subjects aged over 30 years. The crowns were divided longitudinally into two halves (mesial and distal). The cut surface of each half was lined with nail polish. Group I: teeth were subjected to bleaching agent according to manufacturer instructions. In Groups II, III & IV teeth samples were subjected to Nano-hydroxyapatite for 60 min. before, during and after the bleaching treatment respectively. Scanning electron micrographs of the enamel surface and subsurface were obtained and evaluated descriptively. The enamel chemical characterization of the samples was performed by the Scanning Electron Microscope equipped with microanalysis EDXA Element. Results: All experimental groups showed apparently more morphologically intact surface with variable percentage of surface precipitates. Group III and IV showed positive trials to improve the subsurface enamel structure in which Nano-HA particles binding to enamel structure with no statistically significant change in Ca/P. Conclusions: the incorporation of Nano-HA particles to the bleaching agent didn't cause relevant chemical alterations of the enamel structure mean while it showed a detectable enamel surface and subsurface morphological preservation.