Kong and Sanjayan [23] reported a 25% reduction in compres- sive strength of 25 mm cube metakaolin based geopolymer paste specimens after 10 min exposure at 800 oC. Cheng and Chiu [24]conducted tests on 10 mm thick small geopolymer panels made of metakaolin and granulated slag filler. One side of the panel was exposed to 1100 oC heat and the temperature on the other side was measured as 350 oC after 35 min. As a relatively new material, test results on the behaviour of fly ash based geopolymer concrete subjected to fires at different temperature are scarce in literature. Some initial studies [25,26] showed that fly ash geopolymers gained strength at exposure to relatively low temperature heat such as 200 oC and lost strength at exposure to heats of higher tem- perature. Therefore, a comprehensive study was conducted to understand the changes that occur in low-calcium fly ash based geopolymer concrete when subjected to fires at higher tempera- tures. This paper presents a study on the behaviour of geopolymer concrete specimens exposed to fires at temperature up to 1000 oC. The specimens were exposed to fires of different peak tempera- tures following the heating rate of ISO 834 [27] fire curve in a gas fired furnace. The peak temperature was maintained for certain duration and then the specimens were cooled down to room tem- perature. The extent of heating inside the specimens and the resulting cracking and spalling were observed before conducting the compression tests to determine the post-fire residual strengths. Companion OPC concrete specimens were subjected to fires of same temperature profile and tested similarly. Compari- sons are then made between the results obtained for the two types of concrete experiencing the same fire exposure.