The effect of temperature on the hydration of portland cement blended with 20% of metakaolin is studied in a temperature range of 5 to 40°C. Temperature affects microstructure, phase assemblage, and transport properties. Temperature shows a strong influence on the microstructure at early age in both systems because it enhances the reactivity. At late age of hydration, the inner product formation of the blended system is less developed at higher temperature. The hydrated phase of the blended with metakaolin is more sensitive to the temperature than the plain system. In particular, the AFm and AFt phases vary depending on the temperature. The microstructure governs the transport properties of cements; the blended system shows a lower bulk conductivity. The reactivity of metakaolin is slow at lower temperatures resulting in a high bulk conductivity at early age in the blended system.