Using solid waste materials in the production of construction materials has received considerable attention across the world. The present study investigates the feasibility of using the densified mixture design algorithm (DMDA) method to incorporate unground rice husk ash (URHA) as a partial fine aggregate replacement (0%–40%) in the production of eco-friendly construction bricks. Fly ash (FA) and residual rice husk ash (RHA) are the main binder materials considered in this study. Solid bricks of 220×105×60 mm in size were prepared in accordance with official Vietnamese product standards in steel molds under 35 MPa forming pressure. After casting, the brick samples were stored at 35⁰C and a relative humidity of 50% until the ages required for testing. The brick samples were checked for dimensions and visible defects. The effects of URHA content on the engineering properties of the solid bricks, including compressive strength, flexural strength, water absorption, bulk density, and void volume, were also investigated. The test results showed that all brick samples exhibited good physical and mechanical properties. Compressive strength and flexural strength ranged, respectively, between 20.9–31.5 MPa and 5.7–6.7 MPa. All of these values were significantly better than the values required by the official Vietnamese standards. The results of this study demonstrate a significant potential for applying URHA in the production of eco-friendly construction bricks.