Objective Increased hemoglobin (Hb) levels are known to be associated with increased cardiovascular events and mortality in hypertensive patients, but the underlying mechanism remains unclear. However, an increased Ambulatory Arterial Stiffness Index (AASI), the surrogate maker of arterial stiffness, has been proven to be an independent predictor of cardiovascular disease. This pilot study evaluated the association between Hb and AASI in untreated essential hypertensive patients without anemia. Methods A total of 566 untreated essential hypertensive patients without anemia were divided into Normal-Hb and High-Hb groups according to their Hb levels. The AASI and its symmetric calculation (Sym_AASI) were derived from 24h-Ambulatory Blood Pressure Monitoring (24h-ABPM). A multivariable linear regression analysis was performed to determine the relationship between Hb and AASI, Sym_AASI. Results High-Hb group (n=127) showed higher AASI and Sym_AASI (0.51 +/- 0.11 vs 0.43 +/- 0.12, p<0.001; 0.33 +/- 0.10 vs 0.27 +/- 0.08, p<0.001) compared to Normal-Hb group (n=439). Univariate correlation analysis showed that Hb levels were positively related to AASI and Sym_AASI values (r=0.459, p<0.001; r=0.353, p<0.001). After adjustment for age, sex, BMI, current smoker, eGFR, uric acid, total cholesterol, high-density lipoprotein, 24h-SBP, 24h-PP and dipper status, Hb persisted as a independent determinant of AASI and Sym_AASI (beta=0.402, p<0.001 and beta=0.298, p<0.001, respectively). Conclusion High hemoglobin seems be to associated with increased AASI in untreated essential hypertensive patients without anemia.