The time rate of blood pressure (BP) variation indicates the speed of BP fluctuations. Previous studies have demonstrated that the time rate of BP variation was associated with target organ damage. However, the association between time rate of BP variation and endothelial function has not been evaluated.24-hour ambulatory blood pressure monitoring (ABPM) was performed in 61 patients with metabolic syndrome. Time rate of BP variation was calculated from BP recordings of ABPM. Endothelial function was assessed using reactive hyperemia-peripheral arterial tonometry index (RHI) by EndoPat2000. Multiple linear regression models were used to detect the association between time rate of BP variation and RHI.Among all the subjects (n = 61), the multiple linear regression models revealed that the daytime rate of systolic blood pressure (SBP) variation was independently associated with RHI (β = -0.334, P = 0.008). A 0.1 mmHg/minute increase in the daytime rate of SBP variation correlated with a decline of 0.20 in RHI. The same effect was also found in the subjects with eGFR ≥ 60 mL/ (minute*1.73 m(2)). A greater association was found in those who were not taking a statin, β-blocker, ACEI/ARB, or diuretic and those without diabetes compared with those with any antihypertensive medication or with diabetes. Other ambulatory blood pressure parameters and central hemodynamics were not found to be associated with RHI.Our findings have shown that the daytime rate of SBP variation was associated with endothelial function in patients with metabolic syndrome, independent of other BP parameters and central hemodynamics.