Prolonged exposure of concrete to high temperatures, as in fire occurrences, can cause physio-chemical changes that reduce strength and durability, as well as degradation to the microstructure. Geopolymer has emerged as an alternative binder for concrete that is fire-resistant due to its inorganic base and ceramic-like properties. Notwithstanding the high fire resistance of geopolymer concrete, its application in buildings has to consider potential deficiencies during fire occurrences. The present study evaluates the residual compressive strength and microstructural properties of fly-ash-based geopolymer concrete with exposure to fire at burning temperatures of 500 and 1200 °C relative to OPC-based concrete. Increment in mechanical strength for geopolymer concrete were observed during the exposure to fire at 500 °C due to further geopolymerization but eventually reduced in strength at 1200 °C. The matrix of the geopolymer concrete is denser, hence indicating a higher structural integrity relative to OPC-based concrete, as well a higher thermal stability. © 2022