Abstract Acacia nilotica is used in traditional formulation in Nigeria for the treatment of infectious diseases. The susceptibility of bacteria strains against Acacia nilotica leaves extracts was determined using the disk diffusion method. The result showed A. nilotica leaves to possess antibacterial activity against S. typhi, P. aerugonisa, E. coli and S. aureus. At the highest extract concentration (120 mg/ml), the most susceptible microorganism was E. coli, while the least susceptible was S. typhi. Antibacterial activity of column fractions of A. nilotica revealed fraction 4 to have the highest activity of 9, 10, 14 and 1mm zones of inhibition against the test organisms respectively. Phytochemical analysis revealed the presence of saponins, terpenoids, flavonoids, phenols, carbohydrates, tannins and steroids. This study validates and supports the use this plant in the treatment of infectious diseases.