This paper presents the results of experiment conducted to evaluate the effects of sustained elevated temperature on concrete. In this experiment, concrete with 4 types of cement, low-heat portland cement, blast-furnace slag cement and fly-ash cement were tested for strength without seal after sustained temperature exposure in the range of 20 to 300°C. Compressive strengths did not decline linearly with temperature and were minimal at around 50°C, showing 20% reduction, which associated with inter-mediate weight loss of 3%. Reductions in tensile strength and modulus of elasticity were greater than compressive strength.