Two constituents were isolated as the antibacterial principles from the methanolic extract of Crassirhizomae Rhizoma against Streptococcus mutans OMZ176 which is known to be a strong cariogenic bacterium. They were identified as flavaspidic acid PB and flavaspidic acid AB by means of physicochemical methods. They exhibited strong antibacterial activity and the minimal inhibitory concentration(MIC) value was 6.3${mu}g$/ml