In this report, metakaolin based-geopolymer foams reinforced with carbon fibers have been prepared for thermal insulating purpose. Potassium silicate and potassium hydroxide solutions were used as activating agents while hydrogen peroxide was used as a pore former. In order to improve chemical interfacial adhesion with the matrix, the carbon fiber was pre-oxidized using 3 M of nitric acid solution for 10, 30, 50 and 70 min. It was found that variation in treatment time did not cause significant difference in neither mechanical nor thermal conductivity. However, both flexural strength and fracture toughness were significantly improved when the geopolymer foams were reinforced with carbon fibers while thermal conductivity was increased by about two times. The prepared geopolymer foams showed promising results to serve the designed purpose. Keywords: metakaolin based-geopolymer foam, carbon fiber reinforcement, oxidation treatment, mechanical and thermal properties.