With the increase in the diversity of applications, the effect of environmental conditions on the mechanical properties of polymeric composites have become more valuable due to the sensitivity of polymers to aging. In this study, an experimental investigation was carried out to study the seawater aging effect on the flexural and low-velocity impact behavior of glass/aramid/ epoxy hybrid composites. Four types of composite groups that are [G 6 ] S , [A 6 ] S , [G 3 A 3 ] S , [A 3 G 3 ] S manufactured by vacuum infusion method were immersed in seawater at 25 °C and 70°C for 1000 h. Mechanical tests were conducted under three different conditions, namely, dry, wet, re-dried. As temperature increases, the water gain ratio also increases for all composite groups. Flexural strength was significantly reduced with seawater absorption for the wet state tested groups at each temperature. The reductions in flexural strength of the re-dried test groups are less than in the wet state test samples. Charpy test results showed that as the composite groups were exposed to hydrothermal aging, the impact strength of the plain glass/ epoxy, GAG/epoxy, and AGA/epoxy hybrid composite decreased. SEM analysis showed that as temperature increases, delamination and fiber/matrix cracks also increases.