A new guaianolide, 1S, 3S, 5R, 6S, 7S, 11R-l-hydroxy-11α,13-dihydrozaluzanin C (1), was isolated from Moquiniastrum polymorphum subsp. floccosum trunk bark, together with fifteen known compounds, which were identified as 11α,13-dihydroglucozaluzanin C (2), 8α-hydroxy-11α,13-dihydrozaluzanin C (3),