Abstract In this work, the opportunity of employing crystalline silica in the form of quartz powder (QP) to increase the fire resistance of alkali-activated slag (AAS) has been explored. The ground granulated blast-furnace slag (designated as slag) was partially replaced with QP at levels changed from 5% to 30% with a step of 5%, by weight. After curing for 28 days, the specimens were subjected to elevated temperatures varying from 400 oC to 1000 oC with a step of 200 oC for 2 h. The compressive strength before and after heating was measured. The new formed phases were evaluated by using X-ray diffraction (XRD), whilst the decomposition phases were evaluated by using thermogravimetric (TGA). The changes in the microstructures were monitored by using scanning electron microscopy (SEM). The results showed a positive effect of incorporation of QP, up to 30%, in AAS system before and after exposure to elevated temperatures.