The aim of this study was to investigate the effects of seawater on the failure mode, first failure load and bearing strength behaviour of the pinned joint of fibreglass-reinforced woven epoxy composite prepregs. The specimens were kept in seawater for 3- and 6-month periods. After each period, their mechanical properties were examined. The edge distance-to-upper hole diameter (E/D), the two hole-tohole centre diameter (K/D), the distance from the upper or the lower edge of the specimen to the centre of the hole-to-hole diameter (M/D), and the width of the specimen-to-hole diameter (W/D) ratios were selected as parameters. Moreover, the finite element models of the specimens were developed using ANSYS software, and the Tsai-Wu criterion was used to obtain the first failure load. The numerical and experimental results were compared and were found to be in good agreement for the first failure load.