The objective of this study is to investigate the production of geopolymer bricks using fly ash, with partial replacement of fine aggregate by Basic Oxygen Furnace (BOF) slag, termed as steel slag sand (SSS), a by-product of the Iron and Steel Industries. This study addresses the limited research on SSS as a fine aggregate in geopolymer matrices by exploring three replacement levels (40, 50, and 60%). The impact on physical properties (water absorption, bulk density, and flow value) and mechanical properties (compressive strength and flexural strength) was assessed. Additionally, microstructural, mineralogical, and morphological analyses were performed using XRF, XRD, FT-IR, and SEM techniques. Results indicate that increasing SSS content raises water absorption and bulk density, while decreases the flow value. The optimal mix, with 50% SSS, achieved compressive and flexural strengths of 35 MPa and 5.5 MPa, respectively. Higher SSS levels led to reduced strengths. The study demonstrates that Steel Slag Geopolymer Bricks (SSGB) support a circular economy by utilizing industrial waste and reducing energy consumption.