This paper presents the results of an experimental program that was carried out to investigate the performance of geopolymer (GP) mortar mixes subjected to elevated temperature. The main investigated parameters were the molarity levels of NaOH(6M, 10M, 16M and 20M), the sodium silicate to sodium hydroxide solution ratios (1, 2.5 and 4.5), the alkaline liquid to fly ash ratio (0.40, 0.5 and 0.6), the curing temperatures ( 25, 60 and 90 oC), the rest period (RP) (0, 24 and 48 hours) and extra water (0.1, 0.125 and 0.15). Parallel to preparing the different GP mortars, ordinary Portland cement mortar was made to compare results. The hardened GP and OPC mortars were subjected to different elevated temperatures of 200, 400, 600, 800, 1000 oC for two hours. The properties of GP mortars including the compressive strength and the loss of weight were studied. The residual compressive strengths of the GP samples ranged between 60.1% and 90.9% after exposure to 1000 oC of the compressive strength before exposure to elevated heat temperature, whereas, it reached zero% for OPC samples after exposure to 800 oC. On the other hand, an inverse relationship between the compressive strength with the used extra water was recorded. Moreover, another inverse relationship between alkaline solution to fly ash ratio and the compressive strength was noticed. The GP mortars showed also relatively lower mass loss values compared with OPC specimens which agree well with the residual strength results. later. Otherwise, use this document as an instruction set. The electronic file of your paper will be formatted further at IEEE. Paper titles should be written in uppercase and lowercase letters, not all uppercase. Avoid writing long formulas with subscripts in the title; short formulas that identify the elements are fine (e.g., "Nd–Fe–B"). Do not write “(Invited)" in the title. Full names of authors are preferred in the author field, but are not required. Put a space between authors' initials. Define all symbols used in the abstract. Do not cite references in the abstract. Do not delete the blank line immediately above the abstract; it sets the footnote at the bottom of this column