Antimicrobial activities of three different extracts from experimentally prepared scute decoction, commercial scute decoction and an extract from Scutellaria baicalensis were evaluated and their inhibitory potencies were compared. Both the extracts from scute decoction and Scutellaria showed rather strong antimicrobial activities against E. coli and St. aureus at the low concentration of 2.5 mg/ml. On the other hand, the extract of commercial scute decoction was found to show an inhibitory effect at higher concentration (75 mg/ml). All preparations did not inhibit the fungal growth of Aspergillus niger. Both Sh. dysenteriae (Subgroup A) and Sh. boydii (Subgroup C) which were used for determination of the strain differences in Shigelia spp. had almost the same susceptibility to the extract from sucute decoction.