The concentrations of serum lipids, lipoproteins and apoprotein AI, B100, CⅡ and CⅢ are determined in 32 obese children and age- and sex-matched healthy children. This study aims: 1. to know whether obesity can affect the levels of serum lipids and apoproteins. 2. to understand the correlation between degree of obesity and serum lipids and apoproteins. 3. to study the mechanism of change of serum lipids. In obese subjects, the levels of HDL-C, APO-AI, HDL-C/TC and APO-CⅡ/CⅢ decreased significantly and are negatively correlated to degree of obesity. The levels of TG, VLDL-C, APO-B100, APO-CⅡ and atherosclerosis index increased significantly and are positively correlated to degree of obesity. The levels of cholesterol, LDL-C and APO-CⅡ revealed no change. Multiple correlation analysis showed that TSFT was closely related to HDL-C, STR was closely related to VLDL and APO-C Ⅱ/CⅢ. The mechanism of change of serum lipids and apoprotein is disscused. These results suggest: 1) Obesity can affect the levels of serum lipids and apoproteins. 2) The change of apoprotein and regional fat distribution is a major cause of change of serum lipids. 3) Obese children are at risk to atherosclerosis.