Bioassay-guided fractionation of a methanol extract of Ganoderma lucidum gave a pure cholesterol esterase inhibitor. On the basis of spectroscopic analysis and comparison with data from the literature, the structure of this compound was identified as $5{alpha},8{alpha}$-epidioxyergosta-6,22-dien-$3{et}$-ol (compound I). This compound inhibited cholesterol esterase activity with an $IC_{50}$ value of $42{mu}M$. Lineweaver-Burk plot analysis revealed that compound I is a noncompetitive inhibitor. The findings of this study suggest that compound I may be the active principle of the hypocholesterolemic effect of Ganoderma lucidum.