Feeding flavonoid-rich blueberries to spontaneously hypertensive stroke-prone rats (SHRSP) lowers blood pressure. To determine whether this is due to inhibition of angiotensin-converting enzyme (ACE) activity, as seen with other flavanoid-rich foods, we fed blueberries to SHRSP and normotensive rats and analyzed ACE activity in blood and tissues. After 2 weeks on a control diet, the hypertensive rats showed 56% higher levels of ACE activity in blood as compared with the normotensive rats (p < 0.05). Feeding a 3% blueberry diet for 2 weeks lowered ACE activity in the SHRSP (p < 0.05) but not the normotensive rats. ACE activity in plasma of SHRSP was no longer elevated at weeks 4 and 6, but blueberry feeding inhibited ACE in SHRSP after 6 weeks. Blueberry diets had no effect on ACE activity in lung, testis, kidney, or aorta. Our results suggest that dietary blueberries may be effective in managing early stages of hypertension, partially due to an inhibition of soluble ACE activity.