Non-dipper hypertension is associated with increased cardiovascular risk and target organ damage. Although endothelial dysfunction and arterial stiffness contribute to impaired nocturnal blood pressure decline, their relationship with the Endothelial Activation and Stress Index (EASIX) remains unclear. This study aimed to evaluate the association between nocturnal dipping status, EASIX score, and arterial stiffness. This retrospective study included 163 newly diagnosed hypertensive patients who underwent 24-hour ambulatory blood pressure monitoring and were classified as dipper or non-dipper based on nocturnal systolic blood pressure decline. Arterial stiffness was assessed using pulse wave velocity (PWV), and EASIX was calculated from lactate dehydrogenase, creatinine, and platelet count. Logistic regression analysis was performed to identify independent predictors of non-dipper status, while receiver operating characteristic analysis evaluated the diagnostic performance of EASIX, PWV, and their combination. Seventy-two patients were classified as non-dippers and 91 as dippers. Non-dipper patients had significantly higher EASIX scores (0.73 vs. 0.52, p < 0.001) and PWV values (7.92 vs. 7.05 m/s, p = 0.003). In multivariable analysis, EASIX (OR: 2.553, 95% CI: 1.568–4.156, p < 0.001) and PWV (OR: 1.358, 95% CI: 1.090–1.691, p = 0.006) remained independently associated with non-dipper status. The combined model demonstrated better discrimination (AUC: 0.755) than EASIX (0.723) or PWV (0.625) alone. Higher EASIX scores and increased arterial stiffness were independently associated with non-dipper status, and the combined use of EASIX and PWV improved predictive performance. EASIX may serve as a simple marker for early risk stratification; however, larger prospective studies are needed.