The mechanical properties of composite laminates play a key role in the success of composite reinforcement method, but various investigations suggest that the stiffness of epoxybased composites is sensitive to the variation of moisture ratio and temperature of the working environment. The aim in this research is to characterize the effect of hygrothermal aged composite patch on the strength of repaired cracks, under mixed mode I/II conditions. For this purpose a reinforced sheet, i.e. a crack fastener hole specimen is examined by using a finite element simulation. The crack tip parameters and fracture characteristics of repaired cracks are determined as a function of the total amount of moisture inside the composite patch. The results of this study show that the performance of composite reinforcement technique depends on the amount of water absorption within the bonded patches.