The purpose of this study is to compare the relative risk of metabolic syndrome (MS) in middle aged adults with different body weights. 155 subjects living in urban Beijing were recruited from 24 neighborhood committees of urban Beijing. They were divided into normal weight, overweight and obese groups according to their BMIs. The general information of the subjects was collected using an interview-administered questionnaire. Standard procedure was followed to measure subject's weight, height and waist. Biochemical parameters (total cholesterol (TC), low- and highdensity lipoprotein cholesterol (LDL-C ; HDL-C), triglyceride (TG), and fasting glucose) and blood pressure were also determined. The results indicated that the systolic and diastolic blood pressure, HDL-C of obese group was lower than that of the normal weight group. Fasting glucose of obese males was significantly higher than that of normal weight males. No significant difference of fasting glucose was found among female groups. No significant difference of TG was found among male groups, while TG of overweight and obese females was both significantly higher than normal weight females. There was no significant difference of TC and LDL-C among normal weight, overweight and obese groups in both males and females. The MS rate of obese males was significantly higher than the normal weight and overweight males, as was the female. The relative risk of MS in obese group was about 11 times higher (OR=11.249, $95\%CI$ = 3.812 - 33.191) than the normal weight group after adjusting for age, gender, smoking, drinking, family economic level and education status. It is concluded that obesity contributed to lower HDL-C, hypertriglyceride, hypertension and MS after controlling the effects of age, gender, socioeconomic status, alcohol drinking and smoking. Obese individuals have a higher risk of having MS than their normal weight counterparts.