In severe environments, steel reinforcement is often found corroded, thus decreasing the expected life span of that structure. Fibre Reinforced Polymer (FRP) rebars are the best choice for resisting those corrosive effects. Considering the cost and its properties, Glass FRP (GFRP) rebars are found to be a suitable option for replacing steel rebars in corrosive environments. Those rebars are very effective in tension. The limited strength of those rebars in compression and very scattered strength values make them inferior for use in the compression regions. After being in the concrete for a long time, it will be subjected to an alkali reaction, which will reduce its strength. The behaviour of GFRP rebar in compression after its exposure to an alkali solution has not been explored much. This paper focuses on finding the percentage reduction in compressive strength and elastic modulus when subjected to an alkali solution. Four different diameters of GFRP rebar from the same manufacturer are considered for observing the reduction in strength and elastic modulus. The specimens were cut into two different L/d ratios. Those specimens were immersed in alkali solution for 30 days and 60 days at 60 °C ± 5 °C. It is found from the test results that the resin system present in the rebar degrades with time in an alkaline solution.