The current work aims to investigate the possibility of using fly ash (FA) and residual rice husk ash (RHA) to produce unfired building bricks (UBB) with applying densified mixture design algorithm (DMDA) method.In this investigation, little amount of cement was added into the mixtures as binder substitution.Whereas, unground rice husk ash (URHA), an agricultural by-product, was used (10-30%) as partial replacement of fine aggregate.The UBB of 220×105×60 mm in size were prepared for the tests of dimensions, visible defects, compressive strength, flexural strength, water absorption, bulk density and void volume to evaluate the hardened bricks properties according to related Vietnamese standards.Forming pressure of 35 MPa was applied to form the bricks in the steel mold.The test results reveal that all brick specimens obtained good mechanical properties.Compressive strength, flexural strength and water absorption of the bricks were respectively in range of 15.1-22.1 MPa, 2.3-3.5 MPa and 9.5-17.3% while the other properties of the bricks were well conformed to corresponding Vietnamese standards.Furthermore, it was definitely proved many potential applications of FA and RHA in the production of UBB with small amount of cement substitution.