Corrosion is a significant problem for concrete constructions exposed to harsh conditions, as reinforcement bars can deteriorate rapidly. Due to its great corrosion resistance and lightweight qualities, glass fiber reinforced polymer (GFRP) is a viable alternative for steel reinforcement in concrete buildings. The bonding strength between concrete and GFRP bars is crucial to the stability and durability of concrete buildings. Bond strength is affected by a number of factors, including concrete compressive strength, bar diameter, embedment length, concrete cover, bar position, and bar surface characteristics. This study investigates the impact of elevated temperatures on the adhesive strength between GFRP bars and concrete. Twenty-four pullout tests were performed on 150 mm concrete cubes utilizing GFRP bars of three different diameters (10, 12, and 16 mm) and an embedment length of 100 mm. Twelve specimens had GFRP bars in the core, while the other Twelve had bars at the surface with a clear cover of 40 mm. The specimens were subjected to high temperatures of 400°C for 90 minutes. After cooling to room temperature, the binding strength of the GFRP bars was assessed. Bond strength fell by 25.5%, 36.21%, and 54.1% with rising temperature for GFRP bars with diameters of 10, 12, and 16 mm, respectively, when the bars were in the middle of the specimens. Larger diameter bars showed a greater loss in binding strength. On the other hand, altering the stress type in concrete from tension to compression close to the cube surface lowered the decrease in binding strength to 33%, 29.81%, and 36.8%, respectively, for the same bars when their location was adjusted to be close to the cube surface.