A new monocyclofarnesane-type sesquiterpenoid, hostasolide A (1), along with five known compounds, lyciumide A, feruloyltyramine, dimethyl 4,4'-dihydroxy-3,3'-dimethoxy-beta-truxinate, 4-hydroxy3-methoxybenzaldehyde, and 3,4-dimethoxycinnamic acid, were isolated from the whole plant of Hosta ensata. The structure of compound 1 was determined on the basis of spectroscopic analysis. The inhibitory activities of compound 1 against acetylcholinesterase, human chronic myelogenous leukemia K562 cells, and human breast cancer MCF-7 cells were also evaluated.