Objective To investigate the relationship between oxidative stress and lipid metabolism characteristics in elderly patients under different status of thyroid function. Methods Eighty-six newly-diagnosed elderly patients with thyroid diseases,83 non-elderly patients with thyroid diseases and 20 normal subjects as control were selected.and 47 hyperthyroidism and 39hypothyroidism in elderly,43 hyperthyroidism and 40 hypothyroidism in non-elderly were diagnosed according to diagnostic criteria of the thyroid disease.The levels of fasting plasma malondialdehyde(MDA),superoxide(SOD)and oxidized low density lipoprotein(OX-LDL)were measured by thiobarhiturates,colorimetric method and enzyme linked immunosorbent assay(ELISA).Meanwhile,lipid profile and thyroid function were also measured,SOD/MDA ratio was calculated. Results Lipid profiles in the elderly hyperthyroidism group were significantly higher than those in the non-elderly group(P＜O.05 or P＜0.01)but were significantly lower than those of normal control group(P＜0.05 or P＜0.01).The plasma MDA[(10.23±6.29)μmol/L vs.(3.66±2.53)μmol/L vs.(7.37±4.58)μmol/L],free fatty acids(FFA)[(0.86±0.58)mmol/L us.(0.45±0.12)mmol/L vs.(0.61±O.46)mmol/L]and SOD levels were significantly higher in elderly patients with hyperthyroidism than in normal control and non-elderly hyperthyroidism groups(P＜0.05 or P＜O.01).In the patients with hypothyroidism,the plasma MDA[(9.03±5.98)μmol/L vs.(6.59±3.18)μmol/L vs.(3.66±2.53)μmol/L],OX-LDL[(387.36±71.04)μg/L vs.(355.22±45.01)μg/L vs.(324.53±56.19)μg/L],TC,LDL-C,non-HDL-C,LP(a) and Apo-B100 levels were significantly higher in the elderly group than in the non-elderly and normal control groups(P＜0.05 orP＜0.01).The SOD/MDA ratio was significantly lower in the elderly patient groups with hyperthyroidism or hypothyroidism than in normal control and non-elderly groups(all P＜0.01).In a multiple step-wise regression analysis.FT4 and FFA were independent factors related tO MDA in hyperthyroidism group,and non-HDL-C and LDL-C were independent factors related to MDA inhypothyroidism group. Conclusions Serious lipid metabolic disorder exists in newly-diagnosed and untreated elderly patients with hyperthyroidism and hypothyroidism.It is suggested that oxidative stress is obviously strengthened in elderly patients with thyroid function disorder and that the degree of oxidative stress is correlated with lipid metabolic disorder.