This study investigates the effect of unground rice husk ash (URHA) on physical, mechanical, durable properties and microstructural characterization of unfired building bricks (UBB) that were produced using fly ash and sodium hydroxide solution based on geopolymerization technology. The URHA was used to replace 0%, 10%, 20%, and 30% natural chippings. The low forming pressure of 0.5 MPa was applied to produce the brick samples. Experimental results indicate that the compressive strength, unit weight, ultrasonic pulse velocity, and thermal conductivity of brick samples reduced, while their porosity and water absorption increased with increasing the URHA content. Moreover, scanning electron micrographs showed the high porosity and microcracks inside the structure of brick samples containing high URHA level. However, the use of 10% URHA is recommended for the production of UBB with good quality. Besides, 20% URHA can also be used for the production of UBB with the low-quality requirement.