Although careful monitoring of asymptomatic severe aortic stenosis (AS) is recommended to prevent missing the optimal timing of surgical or transcatheter aortic valve replacement, prophylactic treatment that could extend the asymptomatic period remains unknown. In a hypertensive population, high blood pressure (BP) measured at the doctor's office is known to be associated with B-type natriuretic peptide (BNP) level, a surrogate marker for symptomatic deterioration in AS. Little is known regarding the association between nocturnal BP variables and BNP in severe AS with preserved ejection fraction (EF). Methods and Results: The subjects consisted of 78 severe AS patients (mean age, 79±6 years) with preserved EF. Nocturnal BP was measured hourly using a home BP monitoring device. On multiple regression analysis, nocturnal mean systolic BP (SBP) remained independently associated with BNP after adjustment for age, sex, body mass index, estimated glomerular filtration rate, antihypertensive medication class, early diastolic mitral annular velocity, and left ventricular mass index (P=0.03), whereas diastolic BP (DBP) and variables of BP variability were not. Higher nocturnal SBP rather than DBP or indices of BP variability was independently associated with BNP in AS patients with preserved EF. Intervention for nocturnal SBP may therefore extend the asymptomatic period and improve prognosis.