Abstract: Objective To study the associations between body mass index(BMI),age and blood pressure(BP)in Chinese adults.Methods A cross-sectional study was carried out among 79 012 Chinese adults aged 20-80 years in Beijing and Chongqing municipality.The distributions of BMI and BP were described by age and gender.Pearson correlation analysis and logistic regression were used.Results The mean BMI was lowest in the adults aged 20-29 years,with the average values of 23.9±3.5 kg/m² and 20.6±2.5 kg/m² for the men and women,respectively.The highest BMI was 25.5±2.9 kg/m² for the men at the ages of 40-49 years and 24.6±3.3 kg/m² for the women of 60-69 years old.Mean systolic BP was higher among the adults with elevated BMI and those with older age;the mean diastolic BP was the highest(81.6±11.8 mm Hg)for the men at the age of 50-59 years and that(76.5±11.5 mm Hg)for the women at the age of 60-69 years.Correlation analysis results showed that BMI was positively correlated with systolic BP and diastolic BP(r=0.349,0.318,P<0.001);age was also positively related to BMI,systolic BP,diastolic pressure(r=0.194,0.454,0.226,all P<0.001).The odd ratios (ORs) of prehypertension,stage I and stage II or above hypertension for the overweight adults were 1.94,2.91,and 3.70 and the ORs for obesity adults were 3.31,7.62,and 12.24 compared to the adults with normal BMI.Conclusion Aging and obesity can increase the risk of hypertension.These results imply the need to develop strategies for early prevention and control of hypertension in Chinese adults.