The antibacterial activity of 31 chalcones was tested against bacterial strains, Bacillus cereus ATCC 11778, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 25923. Some of the tested chalcones showed fair to significant activity against Gram-positive bacteria. By comparison of the results obtained, the antibacterial activity can be related to features such as the presence of a C-4 hydroxyl group, a C-4' oxygenated substituent or a C-3' isoprenoid side chain, while the C-2' hydroxyl group might have importance for the stability of the molecule. The inhibitory effect of chalcones on human pathogenic microorganisms can be correlated with the substitution patterns of the aromatics rings.