This research investigates the properties and hydration of blended cements with rice husk ash. A reference sample and three cements replacement 5%, 10% and 20% weight % rice husk ash were tested. Setting time, flowability, pozzolan activity index, autoclave expansion, compressive strength and flexural strength were measured. The hydrated products were identified by X-ray diffraction. The microstructure of the hardened cement paste and their morphological characteristics were examined by scanning electron microscopy. It is concluded that the increase of rice husk ash content reduces the cement content in the mix, and the hydration process slows down causing setting time to increase. The calcium hydroxide decreases and the hydration product C-S-H gel increases as a result of the pozzolanic reaction, the microstructure becomes denser and the strength is increased.