Chamaecyparis lawsoniana (A.Murray bis) Parl., known as Port Orford cedar or Lawson cypress and Thuja plicata Donn ex D.Don, also called giant arborvitae, are a species of the Cupressaceae family. Multiple significant biological activities of C. lawsoniana and T. plicata essential oils have been widely investigated, but their genotoxic and/or antigenotoxic properties are not well established. In the present study, two in vitro antioxidant assays were performed to assess the possible DNA protective activity of five different concentrations (0.19, 0.38, 0.75, 1.5, and 3%) of essential oils against oxidative damage induced by hydroxyl and peroxyl radicals. According to the obtained results, both essential oils have a remarkable DNA protective activity against hydroxyl and peroxyl radicals induced DNA damage. These findings confirm that C. lawsoniana and T. plicata essential oils in tested concentrations could be valuable candidates for medicinal and pharmaceutical applications.