From the whole plants of Conyza canadensis (Compositae), a new C-10 acetylene, namely 8R, 9R-dihydroxymatricarine methyl ester (1), and a new triterpenoid, namely 3${eta}$ 16${eta}$, 20${eta}$-trihydroxytaraxast-3-O-palmitoxyl ester (4), were isolated along with eleven known compounds(2, 3, 5-13). The structures of all 13 compounds were elucidated on the basis of their spectral data. The antibacterial activities of compounds 1-3 were evaluated.