Externally bonded fiber reinforced polymer (FRP) laminates are widely used to strengthen and rehabilitate reinforced concrete (RC) structural members in flexure and shear. Despite the clear and proven advantages of using FRPs over traditional materials, the greatest disadvantage to its wide utilization is the limitation in knowledge of the behavior of such composite materials after being exposed to high temperatures. The aim of this paper is to experimentally investigate the variation of mechanical properties in terms of the elastic modulus and tensile strength of composite carbon (C), composite glass (G) sheets and their hybrid combinations (CG) when exposed to different temperatures, ranging from 25C to 300C. All specimens were subjected to the specified temperature level for 45 min and left to cool down for 24 h prior to testing. Stress-strain relationships were plotted and the different observed failure modes were discussed. Based on the test results, the decrease in the mechanical properties of the composite C and G sheets was more severe than those of the composite hybrid CG sheets. In particular, the elastic modulus of the C, G and CG at 250C was reduced by about 28%, 26% and 9%, respectively and their tensile strength at the same temperature was reduced by about 42%, 31% and 35%, respectively, all as compared to room temperature values. Tested specimens failed in brittle rupture of fiber for low range of temperatures (100-150C) and by partial loss of epoxy adhesives followed by sheet splitting for high range of temperatures (200-250C). The calculated values of the mechanical properties of C, G and CG at elevated temperatures can be used as valuable input in computer modeling of RC members strengthened with externally bonded FRP laminates and subjected to elevated temperatures.