The n-hexane extract of Houttuynia cordata was shown to inhibit prostaglandin synthase in vitro. Phytochemical examination led to the identification of five fatty acids (linolenic, linoleic, oleic, palmitic and stearic), cepharanone B, phytol and stigmast-4-ene-3,6-dione. The inhibitory effect of the extract on prostaglandin formation in vitro could be attributed mainly to linoleic and linolenic acid.