In this study, the antimicrobial activities of the RRn extract as well as the rhinacanthin-C against microaerophilic and anaerobic bacteria were evaluated. The microaerophilic and anaerobic bacteria included Streptococcus mutans, Helicobacter pylori and Propionibacterium acnes. Aerobic bacteria including Staphylococcus aureus and S. epidermidis plus yeast (Candida albicans) were also evaluated. Stability of the RRn extract was also studied in order to get useful information for future studies on the development of herbal medicines from the extract.