We established a method to quantify 7-ketocholesterol (7-KC) in low density lipoprotein by using the heparin-citrate method and gas chromatography-mass spectrometry. We examined the concentration of 7-ketocholesterol in LDL using this method to assess the pathological conditions in uremic patients with hemodialysis and healthy controls. We also examined the fatty acid composition in erythrocyte membranes to estimate the modification of biological membranes. We showed that the concentrations of 7-KC/cholesterol in LDL were significantly increased in hemodialysis patients compared to healthy controls (3.68+/-0.45 vs. 2.41+/-0.19, P<0.05) and the ratio of polyunsaturated fatty acids to saturated fatty acids in erythrocyte membranes was significantly decreased in hemodialysis patients compared to healthy controls (0.499+/-0.014 vs. 0.655+/-0. 017, P<0.001). There was no significant difference in 7-KC concentration in LDL or fatty acid composition in erythrocyte membranes between pre- and post-intervention of hemodialysis. We concluded that hemodialysis patients are under oxidative stress, which modifies LDL and erythrocyte membranes and we speculated these modifications may participate in the process of atherosclerosis. We believe that the method to quantify 7-KC in this study is concise and reliable and may be used to investigate various diseases.