Diabetic cardiomyopathy (DCM) is a distinct myocardial disorder that develops independently of coronary artery disease and hypertension and represents a major contributor to heart failure in patients with diabetes. Beyond hemodynamic alterations, DCM is driven by complex molecular mechanisms involving metabolic dysregulation, mitochondrial dysfunction, inflammation, and fibrotic remodeling. Increasing evidence identifies oxidative stress as a central integrative process linking these pathogenic pathways in the diabetic heart. Chronic hyperglycemia, insulin resistance, and altered substrate utilization promote excessive generation of reactive oxygen species, overwhelming endogenous antioxidant defenses and disrupting myocardial redox homeostasis. Oxidative stress induces direct damage to lipids, proteins, and DNA while simultaneously activating redox-sensitive signaling pathways that amplify inflammation, endothelial dysfunction, cardiomyocyte apoptosis, and fibrosis. In addition, epicardial and visceral adipose tissue have emerged as active contributors to myocardial oxidative stress through paracrine and systemic mechanisms, reinforcing inflammatory and fibrotic crosstalk. This review provides a comprehensive overview of the molecular sources and targets of oxidative damage in DCM, examines the impairment of antioxidant defense systems, and discusses emerging therapeutic strategies aimed at restoring redox balance.