Casearia sylvestris Sw., also known as "guaçatonga," is a medicinal plant with broad use in South America. Among the popular applications attributed to this plant are anti-inflammatory, anticancer, antimicrobial, and antiulcer activities. Despite the broad popular use of this plant as a phytopharmaceutical agent, there are few studies about the antimicrobial potential of guaçatonga. In this work, we have studied the antimicrobial potential of an ethanol extract obtained from C. sylvestris leaves against three yeasts, two filamentous fungus, six Gram-negative bacteria, and two Gram-positive bacteria. Through two chromatographic steps using a Sephadex LH-20 column and RP-HPLC, we isolated and characterized two derived compounds of gallic acid: isobutyl gallate-3,5-dimethyl ether (IGDE) and methyl gallate-3,5-dimethyl ether (MGDE). Both compounds showed antimicrobial activity. IGDE was much more efficient than MGDE in inhibiting yeasts (Candida albicans, Candida tropicalis, and Candida guilliermondii) and Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus). This fact is probably associated with the higher hydrophobicity degree of IDGE compared with MGDE. [ABSTRACT FROM AUTHOR]