Recent developments in biomedical science have shown that free radicals are involved in many diseases. They attack the unsaturated fatty acids in the biomembrane resulting in membrane lipid peroxidation, which is strongly connected to aging, carcinogenesis and atherosclerosis. Free radicals also attack DNA and cause mutation leading to cancer. In addition lipid peroxidation is an important factor of deterioration in the processing and storage of food. Therefore, it is important to search for new effective radical scavengers (Sci. Rev. 2 (1997) 152; J. Nat. Prod. Rev. 63 (2000) 1035). In this manuscript we describe the antioxidant activity of new thioureidic compounds.