Antioxidants are compounds that can delay, inhibit, or prevent the oxidation of materials that can be oxidized by scavenging free radicals and help in diminishing oxidative stress. They belong to different chemical classes. Recently there are studies related to pyridazinone derivatives for their antioxidant activities. Since there are evidences implicates reactive oxygen species and nitric oxide as mediators of inflammation and/or tissue damage in inflammatory and arthritic disorders it was though that compounds that have both antioxidant and anti-inflammatory activities would have been essential for the inflammatory diseases. Based on these findings a series of 2H-pyridazine-3-one and 6-chloropyridazine analogues that have anti-inflammatory activity was tested in vitro on superoxide formation and effects on lipid peroxidation were determined against alpha-tocopherol. Most of the compounds have strong inhibitory effect on superoxide anion (between 84% - 99%) at 10(- 3) M concentration. In addition, these compounds showed similar activity to alpha-tocopherol at 10(- 3) M concentrations.