A new 11(15-->1)-abeotaxane diterpene, taxumairol K (1), has been isolated from the ethanolic extract of the roots of Formosan Taxus mairei (Lemee & Levl.) S. Y. Hu. The structure of 1 was determined as 9alpha-(benzoyloxy)-2alpha,4alpha- diacetoxy-5beta ,20-epoxy-1beta, 7beta,10beta,13alpha-tetrahydroxy-11(15-->1)-abeota xane on the basis of spectral analysis. Taxumairol K (1) exhibited mild cytotoxicity against HeLa tumor cells.