The effect of temperature on the phase composition and physico-mechanical properties of cement pastes is vital for fire resistance. Addition of fine, divided materials, such as dehydrated aluminum silicate (fired clay), natural hydrated aluminum silicate (clay), chromite, sintered magnesite, slag, silica, fly ash, diatomaceous earth, and Homra (crushed clay bricks), to Portland cement is known to increase heat resistance by combining with lime. Homra is a pozzolanic material that can react with lime liberated from the hydration of ordinary Portland cement (OPC). This reaction improves the microstructure of cement pastes. In this study, OPC was partially substituted by Homra in the ratios of 10, 20, and 30 wt.%. The cement pastes were fired for 3 h without any load at increasing temperatures from 100°C to 600°C by increment of 100°C. The results show that the replacement of OPC by 20 wt.% Homra improves the compressive strength by about 25.0%, but replacement by 10 and 30 wt.%, the strength increases by 4.0% and 8.5% at 600°C. This result is also due to the pozzolanic reaction of Homra with liberated lime to produce additional amounts of calcium silicate hydrates.