The effect of hot-wet environment on the structural properties of composite T-joints reinforced with z-pins is experimentally investigated. The properties of unpinned and z-pinned carbon fiber-epoxy T-shaped joints were determined following conditioning in a hot (75°C) and humid (85% relative humidity) environment for increasing times up to five months. Water absorbed by the z-pinned joint weakened the mode I bridging traction load generated by the z-pins. However, the structural properties of the z-pinned joint were not affected by the hot-wet environment because they are strongly influenced by the friction-induced traction load generated during z-pin pull-out, which was not affected by absorbed water. The effect of water removal by drying on the restoration of the z-pin bridging traction load and the structural properties of the z-pinned joint are also investigated.