Antimicrobial activity and phytochemical constituents of an ethanolic extract of Aegle marmelos were investigated. The phytochemical screening of the crude extract revealed the presence of Alkaloids, Cardiac glycosides, Terpenoids, Saponins, Tannis, Flavonoids, and Steroids. The crude ethanolic extract was tested for antimicrobial activity against gram positive organisms of Bacillus subtilis (NCIM: 3471), Staphylococcus aureus (NCIM: 2079), gram negative Escherichia coli (NCIM: 2065) and Pseudomonas aeruginosa (NCIM: 2200) at different concentrations levels of 0.5, 1.0, 1.5, 2.0 and 2.5 mg/ml. At the 2.5 mg/ml concentration, gram negative Escherichia coli exhibits a zone of inhibition about 25.7 mm; Pseudomonas aeruginosa 19.9 mm; gram positive Staphylococcus aureus 29.0 mm; and Bacillus subtilis, a maximum zone of inhibition about 28.1 mm as compared to the control drug penicillin. Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis exhibit a maximum zone of inhibition, hence they were considered as susceptible to the plant extracts but Staphylococcus aureus doesn’t exhibit such a zone of inhibition and is therefore considered as resistant.