As a result of our previous work, the antimicrobial activity of some benzylidene-bis-(4-hydroxycoumarin) derivatives against certain Gram-positive bacteria was proved [13]. The result of the present study showed a broad range of antimicrobial activity. All of the coumarins exhibited activity against Gram-positive bacteria and fungi, and few of them were selectively active against one or two strains, whilst they displayed no activity against Gram-negative bacteria. Because of the permeability barrier provided by the outer membrane, Gram-negative bacteria are resistant to all of the tested compounds.