Mean platelet volume (MPV), an indicator of platelet activation, has been shown to be elevated in patients with hypertension. However, data available on the association between MPV level and prehypertension are limited. Prehypertension is also associated with an increase in cardiovascular morbidity and mortality. A cross-sectional study was performed among 80 545 standardized medical checkup participants <18 years in age without hypertension or diabetes in China between April 2009 and May 2010. Blood pressure was categorized as prehypertensive (systolic blood pressure, 120-140 mm Hg and/or diastolic blood pressure, 80 to 90 mm Hg, n= 36 586) and normotensive (systolic blood pressure, < 120 mm Hg and diastolic blood pressure, <80 mm Hg, n=43 959). Mean systolic blood pressure and the prevalence of prehypertension increased significantly with increasing MPV. After adjusting for demographics, body mass index, smoking and serum cholesterol, the odds ratio for prehypertension, when comparing the highest category of MPV (>12.0 fl) with the lowest category (<10.1 fl), was 1.08 (95% confidence interval, 1.02-1.13; P for trend=0.014). This association persisted in separate analysis among men but not among women. In nonparametric models, the positive association between MPV and prehypertension appeared to be present across the full range of MPV, without any threshold effect. Increased MPV is associated with prehypertension in a large sample of Chinese adults that are free of cardiovascular disease and hypertension.