The Schiff base derivatives of benzopyran-4-one are characterized by imine groups which have biological activities such as antimicrobial, antifungal and antitumoral. The aim of this study was therefore to evaluate the toxicity of Schiff bases towards bacterial cells. Escherichia coli as Gram-negative bacteria and Staphylococcus capitis as Gram-positive bacteria were exposed to different concentrations of Schiff bases. For assessment of toxicity a 96-well turbidimetric procedure, capable of testing the antimicrobial properties on a single microplate, was used. Analysis of the growth curves showed that the antibacterial effect of these Schiff bases on Gram-negative bacteria was higher than that on Gram-positive. Furthermore the presence of hydroxylic groups is correlated with an increased antibacterial effect.