Fractures in concrete, despite its widespread usage as a construction material, are an inevitable fact of life. As a result, water and other salts can leak through the micro-cracks when the load imposed exceeds the concrete's tensile strength. Corruption and vulnerability to structural failure ensue as a result of this process. When water, CO2, or other chemicals come into contact with reinforcing steel in concrete buildings, cracks occur, reducing the concrete's durability and strength. Cracks can also compromise the structure's structural integrity. To increase the concrete's compressive strength, researchers used microorganisms like Bacillus subtilis in this investigation. Hence, a varying amount of bacillus subtilis is used in the mixes for M20 and M40 grades of concrete and found that the compressive strength of specimens (150 x 150 x 150 mm in size). From the obtained results, it could be concluded that 10 ml of bacteria is optimum to achieve better strength for 7 and 28 days of curing days.