['Childhood hypertension is a complex disease influenced by both genetic and environmental factors. We aimed to examine the effect of interactions of five polymorphisms with physical activity on blood pressure (BP)/hypertension in the Chinese children.', 'A population-based case-control study was carried out in Beijing of China in 2004, which included 619 hypertensive cases and 2458 normal BP controls. Physical activity information was collected through the use of a validated questionnaire, and five polymorphisms were genotyped using TaqMan. In active group, there was no significant association of five polymorphisms and genetic risk score with systolic/diastolic BP (SBP/DBP) and risk of hypertension (all p > 0.05). In contrast, in inactive group, two polymorphisms and genetic risk score were significantly associated with SBP (rs17249754: β = 1.26, 95% confidence interval (CI) 0.61-1.90, p < 0.001; rs1004467: β = 0.68, 95%CI 0.03-1.32, p = 0.039; genetic risk score: β = 1.54, 95%CI 0.74-2.33, p < 0.001); three polymorphisms and genetic risk score were significantly associated with hypertension (rs17249754: odds ratio (OR) = 1.27, 95%CI 1.08-1.49, p = 0.004; rs1378942: OR = 1.25, 95%CI 1.00-1.57, p = 0.050 (marginally significant); rs16998073: OR = 1.17, 95%CI 1.01-1.37, p = 0.044; genetic risk score: OR = 1.38, 95%CI 1.13-1.68, p = 0.001).'] Does physical activity modify the associations between genetic variants and hypertension in the Chinese children?