This research work investigates the effect of rice husk ash (RHA) and grounds granulated blast furnace slag (GGBFS) on the mechanical properties of high-strength concrete (HSC). The HSC with different proportions of RHA and GGBFS have tested the compressive strength at 7, 14, and 28 days, split tensile strength, and flexural strength at 28 days. The ordinary Portland cement was partially replaced by a weight ratio of RHA (10%, 15%, 20%), and GGBFS (10%, 20%, 40%). Experimental work was completed to restore at 20°C and 65 percent relative humidity. A total of 90 cubes, 30 cylinders, and 30 beams were cast for different mixes for compressive strength, split tensile strength, and flexural strength of concrete. The test results reported that of RHA the compressive strength increases by 6.62 percent compared to the conventional mix at 28 days split tensile strength and flexural strength increases by 6.23 and 5.21 percent. Also, the optimum percent of GGBFS compressive strength increases by 6.81 percent, and split tensile strength and flexural strength increase by 6.89 and 5.61 percent. The RHA and GGBFS-based concrete are emerging construction materials with carbon dioxide (CO2) emissions compared to conventional cementitious materials. This research studied to investigate the mechanical strength characteristics of blended with RHA and GGBFS. It was observed that the addition of 30 percent GGBFS in concrete increases the compressive strength by 23 percent compared to the control mix. The experimental results showed the inclusion of GGBFS with RHA to attain compressive strength. It was accomplished that the GGBFS and RHA mixture did tend to form stable concrete.