Abstract This paper presents results from experiments on geopolymer binders, composing of metakaolin (MK) and fly ash (FA) blend as a precursor, specially developed for fire resistance applications. Bending and compression tests were conducted at ambient temperature and after exposure to high temperatures on three batches of geopolymer specimens. Based on mechanical property tests and thermogravimetric analysis, an optimum MK–FA proportion required in geopolymers for achieving optimum performance both at ambient and high temperatures is developed. Data from strength tests is utilized to illustrate that MK-FA based geopolymer specimens exhibit comparable bending and compressive strength as that of ordinary Portland cement specimens both at ambient temperature and after exposure to high temperatures. Thus, MK-FA based geopolymers offer a feasible alternative to conventional Portland cement in practical building applications.