The effects of oxygenated lanosterol derivatives (1-14) on cholesterol biosynthesis from [24-³H]-lanosterol were tested in 10000×g supernatant (S₁₀) fraction of rat liver homogenate (RLH). Among the derivatives studied, 7-oxo-24, 25-dihydrolanosterol (11) was most active in depressing cholesterol biosynthesis from lanosterol. The inhibitory activities of these derivatives on cholesterol synthesis are discussed in relation to the position and stereochemistry of the oxygen group on the side chain and the sterol nucleus.