The work aims to study the effect of substitution of micro-silica (SF) and fly ash (FA) on the behavior of composite cement pastes exposed to elevated temperature. The composite cements are composed of 80 mass% OPC with variable amounts of SF and FA. The fire resistance of composite cement pastes was evaluated after firing at 250, 450, 600, 800oC with rate of heating 3oC/min for 3h soaking time. The physico-mechanical characteristics such as total porosity, bulk density and compressive strength of cement pastes were determined at each firing temperature. Moreover, the phase composition, free lime and microstructure for some selected samples were investigated. Cement pastes containing 10 and 15 mass% have higher firing resistance than all SF-pozzolanic cement pastes at 600oC. It can be also, concluded that the composite cement pastes made from 10% of SF and 10%FA have good fire resistance in comparison with cement pastes made from only SF-pozzolanic cement pastes up to 450oC.