Objectives: this study aims to evaluate the effect of ozone therapy on artificially created carious lesions via Vickers microhardness test. Methods: Ninetyextracted human premolars were collected, coded and randomly allocated into 3 equal groups (n=30). Metallic brackets were bonded to the teeth using TransbondPlus SEP (3M Unitek). Specimens were subjected to demineralizing regimen to induce carious lesions. Then, each group underwent a pH cycling protocol according to each group's remineralizing agent. Group1: ozone; group2: NHA; group3: saliva (control). Enamel surface microhardness is tested using Vickers microhardness tester at baseline and after remineralization to allow comparison. Results& Significance: Ozone-treated group showed the greatest enamel surface microhardness of all.There was significant difference between the ozone-treated group and the control (p < 0.05). However, there was no significant difference between the NHA group and control group (p>0.05). Keywords:remineralization, ozone, nano-hydroxyapetite, microhardness