Obesity and vitamin D deficiency have both been linked to augmented activity of the tissue renin-angiotensin system (RAS). We investigated whether obesity status influenced the relationship between 25-hydroxyvitamin D (25(OH)D) and vascular RAS activity. The levels of 25(OH)D were measured in hypertensive obese (n=39) and non-obese (n=58) Caucasian individuals. RAS activity was assessed by plasma renin activity, and evaluation of the vascular sensitivity to angiotensin II (AngII) using the mean arterial pressure (MAP) response to an infusion of AngII. Among obese subjects, 25(OH)D was an independent positive predictor of the MAP response to AngII (β=0.70, r=0.41, P<0.01); lower 25(OH)D concentrations were associated with a blunted MAP response to AngII. In contrast, 25(OH)D did not significantly predict the vascular sensitivity to AngII in non-obese subjects (β=0.10, r=0.07, P=0.62). A multivariable-adjusted interaction model confirmed that the positive relationship between 25(OH)D and the vascular sensitivity to AngII strengthened with obesity (P-interaction=0.03). These findings demonstrate a positive association between 25(OH)D and the vascular sensitivity to AngII in obese hypertensives, and further suggest that vascular RAS activity may progressively increase when 25(OH)D deficiency occurs in obesity. Future studies to evaluate the effect of vitamin D supplementation on vascular RAS activity in obesity are needed.