Abstract: Medicinal herbs are moving from fringe to mainstream use with a greater number of people seeking for remedies and health approaches from side effects caused by synthetic chemicals. This has aggravated the search for antimicrobials from plants sources. Therefore, this study was aimed at investigating the efficacy of aqueous extract of Moringa oleifera leaves against some clinical isolates (Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa). The study was carried out between January and June, 2014. The Moringa oleifera leaves sample were collected from the Kebbi State University of Science and Technology Aliero Orchard and screened for antimicrobial activity against the isolates using agar well diffusion assay, and preliminary phytochemical analysis were also conducted using standard procedures. Concentrations of the extract used were 30mg, 60mg, 90mg and120mg. The extract demonstrated the highest activity at 120mg, with the zone of inhibition of 28.5mm, 25.5mm and 24.0mm on Salmonella typhi, Escherichia coli and Pseudomonas aeruginosa respectively. The results of preliminary phytochemical screening revealed the presence of Saponins, Tannins, Flavonoids, Glycosides and Alkaloids. The antibacterial assay results portrayed broad spectrum activity of Moringa oleifera leaf extract against the test organisms with the comparable inhibitory zones by standard antibiotic (Ciprofloxacin). In conclusion the results from these findings have shown the antibacterial potentials of Moringa oleifera leaf extract implying that the extract could help as a chemotherapeutic agent or might be a lead compound for the development of new potent antibacterial agents.