Although chemically inert nanosize mineral fillers have been shown to modify early cement hydration kinetics, with the effects dependent upon usage rate, particle size, and dispersibility, the effects of such fillers on the apparent activation energy (E-a) of cement has not been previously examined. Here, cement E-a was calculated from isothermal calorimetry performed at different temperatures with two different types of fillers (i.e., titanium dioxide and limestone) using a linear method as well as a modified ASTM C1074 method. The use of both types of nanoparticles increased the rate of cement hydration as well as accelerated the reaction rate, due to heterogeneous nucleation effect, as previously demonstrated. E-a increased in the presence of nanosized fillers, demonstrating an increased temperature sensitivity of the filler-cement composites relative to ordinary cement. These results show that chemically inert nanoparticles behave fundamentally differently compared with supplementary cementitious materials such as fly ash and silica fume which instead decrease temperature sensitivity. The increased temperature sensitivity could thus be used to modify and optimize the reaction mechanism and kinetics of cement hydration, especially to increase the rate of cement hydration, to decrease setting time, and to achieve faster strength gain accounting for higher or lower temperatures during curing.