Consumption of cholesterol oxidation products (COPs) is a growing health concern, but little is known about the intake of beta-sitosterol oxidation products (SOPs). The present study was performed (i) to compare the oxidative stability of cholesterol with that of beta-sitosterol; (ii) to investigate the oxidative pattern of cholesterol and beta-sitosterol in lard, corn oil, and olive oil; and (iii) to examine the effectiveness of green tea catechins (GTC), alpha-tocopherol, and quercetin in prevention of cholesterol and beta-sitosterol oxidation compared with butylated hydroxytoluene (BHT). Results showed both cholesterol and beta-sitosterol were thermally unstable with 75% of cholesterol and beta-sitosterol being oxidized at 180 degrees C for 2 h. The oxidation behavior of beta-sitosterol was similar to that of cholesterol in terms of oxidative rate and oxidation products. The major COPs produced were 7-ketocholesterol, 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol 5,6alpha-epoxycholesterol, and 5,6beta-epoxycholesterol, whereas the major SOPs were 7-ketositosterol, 7alpha-hydroxysitosterol, 7beta-hydroxysitosterol, 5,6alpha-epoxysitosterol, and 5,6beta-epoxysitosterol. Under the same experimental conditions, both cholesterol and beta-sitosterol were oxidized more slowly in corn oil, lard, and olive oil, attributable to the unsaponified antioxidants present in these fat and oils. GTC, alpha-tocopherol, and quercetin were more effective than BHT in preventing the oxidation of cholesterol and beta-sitosterol.