Anoectochilus formosanus, an orchidaceous plant native to Taiwan, is widely used as a folk medicine in Taiwan and other Southeast Asian countries. We attempted to isolate the bioactive principles from A. formosanus and succeeded in purifying the compounds. Two known compounds (N-cis-feruloyl tyramine and N-trans-feruloyl tyramine) were isolated and both significantly inhibited osteoclast formation, which is important in the development of osteoporosis.