The purpose of this research is to determine the mechanical properties of historic masonry walls retrofitted with Glass Fiber Reinforced Polymer (GFRP) under axial load through experimental method. Four ancient masonry wall specimens were tested under axial load acted at the top surface. Two wall specimens were served as reference without retrofitting. The third wall was retrofitted with GFRP on full surface before loading. The forth wall was strengthened with three GFRP strips before loading. The behaviors of historic masonry walls in Thailand were particular because of their special bond manner and dimension. The tested results demonstrated that the bearing capacity of historic masonry walls was distinctly improved after GFRP strengthening.