The principal objective of this study is to characterize the voids distribution in glass fiber-reinforced unsaturated polyester composites following tempered-water-aging. The main investigation was carried out using micro-computed tomography (µCT) at varying times-and temperatures. The µCT was employed to-assess the damage variations-in the specimens via three-dimensional imaging in order to qualifymand quantify the material’s internal structure after aging at 50 ℃ and 90 ℃ at 15%, 30%, and 60% of total water uptake. The results revealed the presence of cracks with different forms andnfractions in all composite structures in response to hydrothermal conditions. The formation of these fractures in the matrix was found to be directly related to the accumulation of osmotic pressure within microcavities, which is influenced by the moisture concentration. Indeed, an increase in water absorption increases the osmotic pressure, which in turn facilitates crack propagation and interfacial debonding. In this study, it was found that at elevated temperatures and extended exposure times the degradation is more and more accentuated.