The present investigation has been carried out to evaluate the antibacterial activity of ethanolic extracts of Acorus calamus rhizome, Alpinia galanga rhizome, Cinnamomum zeylanicum bark, Piper cubeba fruit, against two gram positive (Bacillus subtilis, Staphylococcus aureus) and two gram negative (Escherichia coli, Klebsiella pneumoniae) organisms respectively. Antibacterial activity was assessed by agar disc diffusion method. The activity of the extracts was measured by zone of inhibition and compared with a standard antibiotic Gentamicin. Among the various concentrations (50, 100, 150 μg/ml), 150μg/ml was found to be very effective. From the data of the results obtained in the present study, it can be concluded that, among the four plants selected, ethanol extracts of Acorus calamus and Alpinia galanga have given scopeful results against the microorganisms selected. Even though the extracts of Cinnamomum zeylanicum and Piper cubeba have antibacterial activity, at low concentration there was no appreciable activity.