The article reviews the role of oxidative stress in neurodegenerative diseases, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Oxidative stress, characterized by an imbalance in redox states, involves excessive production of reactive oxygen species (ROS) or dysfunction of the antioxidant system. The brain is particularly vulnerable to oxidative stress due to its high oxygen demand and the presence of peroxidation-susceptible lipids. Oxidative stress plays a central role in the pathophysiology of neurodegenerative diseases, leading to cellular damage, DNA repair impairment, and mitochondrial dysfunction. Antioxidant therapy has been proposed as a potential treatment, but its efficacy remains inconsistent. The review discusses the measurement of oxidative stress indices, the mechanisms of ROS production in the brain, and the role of antioxidants in neurodegenerative diseases. It also highlights the challenges in evaluating oxidative stress in the brain and the need for better biomarkers to guide therapeutic interventions.The article reviews the role of oxidative stress in neurodegenerative diseases, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Oxidative stress, characterized by an imbalance in redox states, involves excessive production of reactive oxygen species (ROS) or dysfunction of the antioxidant system. The brain is particularly vulnerable to oxidative stress due to its high oxygen demand and the presence of peroxidation-susceptible lipids. Oxidative stress plays a central role in the pathophysiology of neurodegenerative diseases, leading to cellular damage, DNA repair impairment, and mitochondrial dysfunction. Antioxidant therapy has been proposed as a potential treatment, but its efficacy remains inconsistent. The review discusses the measurement of oxidative stress indices, the mechanisms of ROS production in the brain, and the role of antioxidants in neurodegenerative diseases. It also highlights the challenges in evaluating oxidative stress in the brain and the need for better biomarkers to guide therapeutic interventions.