The effect of water absorption on the chemical and mechanical properties of hydrophobic filler containing epoxy matrix composites was investigated by keeping them in distilled water for 9 months. Aerosil R812 (8 nm) and Aerosil R972 (12 nm) were utilized at 3% and 5% w/w filler to resin ratio and the resin/filler mixture was combined with 12-ply carbon fabric to get 15 x 15 cm samples. Samples were molded under a hot press and for each sample 50 test samples obtained by cutting them with a water jet. The obtained samples were characterized by TG, FTIR, and SEM. The effect of water absorption was evaluated by measuring percentage water absorption and flexural strength of samples over 9 months. The results revealed that filler addition lowers the damage created by distilled water a considerable amount and addition of hydrophobic fillers to epoxy matrix composites can be especially beneficial for applications where long-term water exposure is desired.