To determine the cytotoxic activity of natural compounds, chromatographic separation of the hexanesoluble fraction from the fruiting body of Ganoderma lucidum led to the isolation of four steroids and one triterpenoid. They were identified as ergosterol peroxide (1), stella sterol (2), ergosterol (3), 9(11)-dehydroergostrol peroxide (4), and ganodermanontriol (5) based on spectroscopic evidence and physicochemical properties. These compounds were examined for their cytotoxic activity against HL-60, MCF-7, and LLC cancer cell lines. Ganodermanontriol (5) showed cytotoxic activity with IC50 values of 24.8 and 22.9 μg/mL against HL-60 and MCF-7 cancer cell lines, respectively, whereas compounds 1-4 were inactive.