Abstract: This paper is the presentation of flexural strength of concrete beam using hospital waste ash as replacement of cement. The study covered the test of aggregates grading, specific gravity of materials, workability and water absorption as well as the flexural strength test of the composite concrete to determine the suitability of Hospital waste as replacement using constant mix design proportion of 1: 1.64: 2.47: 0.50 in accordance to standard DOE method, with different mixes added based on 0%, 10%, 20%, 30%, and 40% replacement. A total of 75 beams of sizes 450mm × 150mm × 150mm were tested for flexure after the curing period of 3, 7, 28, 60, and 90 days by complete immersion. It shown that the workability of the composite mix decreased with replacement higher than 10%, but density and water absorption increases with replacement level and curing age respectively, while 20% replacement appeared to be the optimum. The study also reveals that,replacement of Hospital Waste Ash under flexural test reduces the flexural strength value as minimum compared to conventional value of concrete. However, it maintains, or slightly reduces the mechanical and durability properties of cement- based materials with cementitious properties that are suitable to be bind together with cement as replacement.