Abstract: Methanol plant-extracts of 221 species from 98 families which had documented uses in Iranian herbal-medicine were screened for antibacterial and antifungal activity against 11 standard bacterial strains and 3 fungal species at 20 mg mlG1. Eighty one samples in 39 families showed antibacterial and/or antifungal activity against at least on one of the tested microorganisms. Antimicrobial activities were evaluated by measuring the diameter of inhibition zones in agar well diffusion method. Dianthus coryophyllus was active against all tested G-ve and G+ve bacteria except Micrococcus luteus. Most susceptible G-ve bacteria were Klebsiella pneumoniae and Bordetella bronchiseptica and least susceptible was Escherichia coli. In G+ve bacteria, most and least susceptible were Staphylococcus aureus and Micrococcus luteus, respectively. Plants with high antifungal activity included Alpinia officinarum, Chrozophora verbasafalia, Cinnamomum zeylanicum, Dianthus coryophyllus, Helleborus nigra, Heracleum persicum, Myrtus communis, Terminalia chebula and Trachysermum copticum which were effective mostly against Candida albicans and C. utilis.