Composites are subjected to different use conditions. Hence, the mechanical properties under different aging conditions are crucial in the composite field. This study aims to investigate the aging effect of a glass/epoxy unidirectional composite in three distinct conditions: mechanical, hygrothermal (hot water), and combined (mechanical and hygrothermal) aging. The composites in the longitudinal [0°] and transversal [90°] directions were molded by RTM with a 37% volume fraction. The aging effects on tensile, compressive, shear, short-beam properties, and dynamic-mechanical characteristics, in 0° and 90° fiber direction, were studied. The aging conditions are affected differently, depending on the property analyzed. Comparing aged and non-aged composites, the tensile (from 380 GPa to 140 GPa and from 80 GPa to 40 GPa for non-aged and combined aging in 0° and 90° directions, respectively) and compressive strength (from 250 MPa to 50 MPa and from 100 MPa to 25 MPa for non-aged and combined aging in 0° and 90° directions, respectively) showed greater relative drop than the elastic modulus (a decrease of 3–4 GPa for all aging analyzed compared to the no-aged composites) due to a deleterious effect on the interface and the chemical aging present in the polymeric matrix attenuates the deleterious effect on it. Besides, the properties measured in the 0° direction were more affected than in the 90° direction with the combined aging the most affected property.