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Background: High adult blood pressure (BP) is an important risk factor for cardiovascular disease (CVD) and mortality. Childhood BP tracks into adulthood. Little is known whether BP trajectories in children have changed over time, as BP is strongly associated with body-size, especially in countries with rapid economic growth. We investigated whether BP trajectories have changed among Chinese children and whether changes can be explained by BMI and height trends. Methods:China Health and Nutrition Survey (eight waves 1991-2011) was used to create four cohorts (7-17y, born in 1981-85, 1986-90, 1991-95, 1996-2000, N=~16000). Multilevel cubic functions were applied to estimate child-to-adolescent trajectories for systolic and diastolic BP (SBP and DBP) with and without adjustment for BMI and height (age-/gender standardised z-scores). Between-cohort differences were examined by testing interactions of each cohort with age terms. Results:Trajectories for SBP increased across cohorts: those for later-born cohorts tended to lay above early-born cohorts in both sexes. After the adjustment differences mean SBP reduced. The reduction was more evident in adolescence (vs childhood) and with adjustment for height (vs for BMI) trajectories. For example, the difference between the last (born 1996-2000) and first (1981-85) cohorts was 1.90mmHg (95% CI: 0.54-3.26) for boys and 2.58 mmHg (95% CI: 1.18-3.98) for girls at 7y, and there was no difference at 16y after adjustments. Similar patterns were seen for DBP.Conclusions:Trends for BP in recent decades among Chinese children and adolescents were partly explained by more rapid growth in height and BMI in later-born children.