Abstract : Vital bleaching is the most minimally invasive strategy for tooth color enhancement, The severity of the side effects of bleaching therapies, such as bleaching sensitivity (BS) or gingival irritation (GI), seems to be related to the dose of peroxide used, the aim of ozone treatment is to eliminate the pain of hypersensitivity after teeth bleaching. The study compared hydrogen peroxide (H2O2) with and without ozone gas (O3) on teeth whitening sensitivity in a split-mouth design with 200 teeth. The teeth were divided into four groups of 50 teeth each: (1) H2O2 only on left upper jaw; (2) H2O2 and O3 on right upper jaw; (3) H2O2 only on left lower jaw; and (4) H2O2 and O3 on right lower jaw. The dental sensitivity levels of the teeth that had undergone bleaching in the four groups were measured 24 hours after the application of ozone gas. We compared the hypersensitivity of patients in four groups: two control groups and two study groups. The study groups had significantly less hypersensitivity than the control groups in both jaws (P = 0.000). The study groups had 88% of patients with no hypersensitivity and 12% with mild hypersensitivity, while the control groups had only 2-6% of patients with no hypersensitivity and 34-46% with mild hypersensitivity. The control groups also had 46-50% of patients with moderate hypersensitivity and 2-14% with severe hypersensitivity, which were absent in the study groups. In Conclusion the application of ozone after H2O2 reduces tissue irritation and sensitivity, and enhances patients’ compliance.