In the current study, the results of antibacterial, antifungal, and antiviral activity tests of four flavonoid derivatives, scandenone (1), tiliroside (2), quercetin-3,7-O-α-L-dirhamnoside (3), and kaempferol-3,7-O-α-L-dirhamnoside (4), are presented. Antibacterial and antifungal activities of these compounds were tested against Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumonias, Acinetobacter baumannii, Staphylococcus aureus, Bacillus subtilis, and Enterococcus faecalis, as well as the fungus Candida albicans by a microdilution method. On the other hand, both DNA virus Herpes simplex (HSV) and RNA virus Parainfluenza-3 (PI-3) were employed for antiviral assessment of the compounds using Madin-Darby bovine kidney and Vero cell lines. According to our data, all of the compounds tested were found to be quite active against S. aureus and E. faecalis with MIC values of 0.5 μg/ml, followed by E. coli (2 μg/ml), K. pneumoniae (4 μg/ml), A. baumannii (8, μg/ml), and B. subtilis (8 μg/ml), while they inhibited C. albicans at 1 μg/ml as potent as ketoconazole. However, only compound 3 displayed an antiviral effect towards PI-3 in the range of 8-32 μg/ml of inhibitory concentration for cytopathogenic effect (CPE). © 2006 Verlag der Zeitschrift für Naturforschung.