The article provides a comprehensive overview of the generation, mechanisms of action, and evaluation of natural antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by normal biochemical reactions, environmental exposure, and dietary xenobiotics, leading to oxidative stress and various diseases. Dietary antioxidants help prevent these diseases by reacting with free radicals in vivo and in vitro. The review discusses the mechanisms of action of natural antioxidant compounds, including enzymatic and non-enzymatic antioxidants, and their ability to scavenge free radicals. It also covers the evaluation of antioxidant activities through various assays, such as superoxide anion radical scavenging, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, total reactive oxygen potential (TRAP), and total antioxidant reactivity (TAR). The article highlights the importance of understanding the reaction mechanisms of antioxidants to develop more effective antioxidants and evaluate their activities. Additionally, it explores the physiological roles of antioxidants, such as uric acid and glutathione (GSH), and the potential of fungal antioxidants. The review concludes by emphasizing the need for further research to understand the mechanisms of free radical scavenging and to derive more potent antioxidants.The article provides a comprehensive overview of the generation, mechanisms of action, and evaluation of natural antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by normal biochemical reactions, environmental exposure, and dietary xenobiotics, leading to oxidative stress and various diseases. Dietary antioxidants help prevent these diseases by reacting with free radicals in vivo and in vitro. The review discusses the mechanisms of action of natural antioxidant compounds, including enzymatic and non-enzymatic antioxidants, and their ability to scavenge free radicals. It also covers the evaluation of antioxidant activities through various assays, such as superoxide anion radical scavenging, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, total reactive oxygen potential (TRAP), and total antioxidant reactivity (TAR). The article highlights the importance of understanding the reaction mechanisms of antioxidants to develop more effective antioxidants and evaluate their activities. Additionally, it explores the physiological roles of antioxidants, such as uric acid and glutathione (GSH), and the potential of fungal antioxidants. The review concludes by emphasizing the need for further research to understand the mechanisms of free radical scavenging and to derive more potent antioxidants.