Objective To evaluate and compare the value of predicting diseases such as hypertension and arteriosclerosis of the body mass index(BMI) and percent body fat(PBF),so as to provide the basis for evaluation of obesity.Methods Totally 3149 common residents in Jiangsu province were surveyed using the method of stratified and cluster sampling.Effective data included height,weight,PBF,blood pressure and brachial-ankle pulse wave velocity(baPWV).Obesity was defined by percent body fat with the evaluation of WHO and ASBP.Areas under ROC curves(AUC)of BMI and PBF were estimated by the nonparametric test and then the two diagnostic tests were compared by predictive value of related diseases.Results(1)Predictive value of BMI to diagnose obesity(defined by PBF):AUC are respectively 0.949(for WHO standard)、0.906(for ASBP standard)in women and 0.864 in men.In age group,the 20-39 years have the highest AUC of BMI to predict obesity.P＜0.01 for above nonparametric tests.(2)According to ROC curves we got the adjusted cut-off points of BMI are respectively 26 kg/m2 in men and 25 kg/m2 in women for WHO standard or 26 kg/m2 in men and 23 kg/m2 in women for ASBP standard,while the specificity of predicting obesity decreased from 90％ ～ 99％ to 76％ ～87％,but the sensitivity significant increased from 17％ ～ 43％ to 78％ ～ 89％;After adjusting the cutoff points of BMI,the value of kappa of prevalence of obesity increased from 0.475 to 0.537 in men and 0.115 to 0.655 in women.(3)To predict hypertension,areas of BMI were 0.688(95％CI:0.656-0.720) in men and 0.745 (95％CI:0.708-0.782) in women,similarly,of PBF were 0.687 (95％CI:0.655-0.718) in men and 0.723(95％CI:0.681-0.764)in women;To predict arteriosclerosis there showed highly consistency that the areas of BMI were 0.613(0.586-0.641)in men and 0.692(95％CI:0.659-0.726)in women,meanwhile,for PBF they were 0.635 (95％CI:0.608-0.663) in men and 0.683 (95％CI:0.648-0.718) in women (P＜0.01).(4) Paired test of the two areas under ROC curves showed that PBF had higher diagnostic value than BMI in men to predict arteriosclerosis(u=2.05,P＜0.05),however,no statistical difference in women(u=0.75,P＞0.05)and in predicting hypertension(u=0.75 to men and u=1.26 to women,P＞ 0.05).Conclusions Using BMI and PBF can all predict hypertension and arteriosclerosis effectively,thus,obesity can be evaluated suitably by both BMI and PBF in large-scale population study,especially in women and youth.Relatively,WHO standard of PBF is more suitable for Chinese population to evaluate obesity than ASBP standard.