Introduction: The loss of tooth structure in natural tooth can be attributed to several aetiological factors like dental caries, traumatic injuries and non carious lesions like attrition, abrasion, erosion. All the lesions result in loss of enamel and dentin which eventually need to be replaced with restorative materials. Aim: To evaluate the effect of different acidic solutions on the surface microhardness of three different nanocomposite restorative materials after one day and six weeks time interval. Materials and Methods: The present in-vitro study comprised of three different composite resin materials, Filtek Z 350 (3M ESPE, St. Paul, USA), Ceram X Mono (Dentsply, Konstanz, India) and Tetric N Ceram (Ivoclar Vivadent, Schaan, Liechtenstein). Twenty four samples were divided into three groups. Group I: Eight specimens of each restorative material were immersed individually in 10 mL of artificial saliva. Group II: Eight specimens of each restorative material were immersed in artificial saliva for four hours and later immersed for five minutes in a tube containing 10 mL of coca cola under stirring and later stored in artificial saliva. This process was repeated for three times a day. Group III: Eight specimens of each test material were individually immersed in artificial saliva for four hours and later immersed in 10 mL of hydrochloric acid (HCl) for five minutes under stirring and later stored in artificial saliva. This process was done three times a day. Vicker’s diamond indenter was used to test the microhardness. Paired t-test, independent t-test, one-way Analysis of Variance (one-way ANOVA) and post hoc test were used for analysis. Results: There was no significant statistical difference (p-value >0.05) in the surface microhardness between all the tested solutions after day 1 time period of Filtek Z 350. There was significant difference of the surface microhardness between all the groups in all the solutions except for Filtek Z 350 and Ceram X Mono in HCl solution at 6 weeks. Conclusion: There was statistically significant reduction in surface microhardness of the three composites immersed in all the three solutions of artificial saliva, coca cola and hydrochloric acid after day 1 and six weeks time interval