Background: A good aesthetic smile is one of the most important factors to attain positive life style. Among various aesthetic treatment modalities available, bleaching gained immense response in aesthetic enhancement. But in some cases, bleaching alone does not fulfill the aesthetic demands which require additional procedures like composites restorations, laminates, veneers etc. However, some of the studies reported that bleaching can alter the microhardness of the tooth, resulting in deficient bonding and demineralisation. The current study was to evaluate the change in microhardness of enamel specimens bleached with 40% hydrogen peroxide gel incorporated with three different nano remineralising agents. Materials and Methods : 30 enamel specimens (5x5x4mm) were obtained from 15 molars and incorporated in acrylic resin mold which were divided into 5 groups (6 per group ).After attaining baseline Knoop microhardness values enamel specimens were subjected to bleaching treatment .Group 1 – control(with no bleaching ) ,Group 2 – Bleaching with 40 % hydrogen peroxide gel, Group 3 – Bleaching with 40 % hydrogen peroxide gel incorporated with Nano calcium chloride, Group/ 4 – Bleaching with 40 % hydrogen peroxide gel incorporated with Nano sodium fluoride, Group 5 – Bleaching with 40 % hydrogen peroxide gel incorporated with Nano hydroxyapatite .Post treatment knoop microhardness values are evaluated and difference between baseline and post treatment microhardness values were obtained. Statistical analysis: Statistical analysis was performed using one‑way analysis of variance and post hoc Tukey’s test. Results: By the obtained values results have been showed that Significant differences were observed between bleaching groups of with and without incorporation of remineralizing agents . The enamel microhardness change in Groups 1, 3, 4, and 5 were significantly lower than that of Group 2 (p < 0.001) Conclusion: : Within the limitations of this study, it can be concluded that incorporation of each one of the three tested biomaterials as remineralizing agents might be effective in decreasing enamel microhardness changes subsequent to in–office bleaching