The present study investigates the compressive strength performance of concrete masonry blocks produced with partial replacement of cement using fly ash and ground granulated blast furnace slag (GGBS). The motivation behind the research is twofold: the need to reduce cement consumption in construction and the necessity of utilizing industrial by-products in a sustainable manner. The work examines four replacement levels, namely 0%, 10%, 20%, and 30%, of cement by fly ash and GGBS. Concrete blocks were cast under controlled laboratory conditions, cured for 7, 14, and 28 days, and subjected to compressive strength testing. The experimental results demonstrated that replacement levels up to 20% generally maintain compressive strength comparable to conventional concrete blocks, while 30% replacement leads to a slight reduction in strength but improves long-term durability and environmental benefits. The study concludes that partial replacement of cement with fly ash and GGBS is a feasible strategy for sustainable block manufacturing without compromising essential strength requirements.