The RRn extract used in this study was standardized by the HPLC method to contain total rhinacantins not less than 70% w/w. The content of rhinacanthin-C, -D and -N in the RRn extract were 71.09, 8.85 and 2.65% w/w, respectively. The total rhinacanthin content of the RRn extract was 82.59% w/w. Antimicrobial activities evaluation of the RRn extract and rhinacanthin-C. found that both of them exhibited antimicrobial activity against S. mutans, P. acnes, S. aureus and S. epidermidis but they were not active against C. albicans at the concentration up to 2000 μg/ml