Fatty acid synthase (FAS) is emerging as a potential therapeutic target to treat cancer and obesity. Bioassay-guided fractionation of a MeOH extract of the rhizomes of Dryopteris crassirhizoma (Dryopteridaceae), using an in vitro FAS inhibitory assay, resulted in the isolation of a series of acylphloroglucinols, as the active principles. The isolates 1-10 inhibited FAS with IC50 values ranging from 23.1+/-1.4 to 71.7+/-3.9 microM. The results of the present study indicate that the acylphloroglucinol derivatives could be considered to be a promising class of FAS inhibitors.