Hypertension is linked to dementia in humans, as well as remodeling and dysfunction in large cerebral arteries. The effects of hypertension on cerebral microvessels, such as penetrating arterioles (PenA), are still unknown. These arterioles are the bottlenecks bridging the pial circulation to the deep parenchymal microcirculation, and they are vital for neurovascular coupling and functional hyperemia. Mineralocorticoid receptor (MR) antagonism reverses hypertension-induced changes in large cerebral arteries. Thus, we hypothesized that MR antagonism will improve PenA dilation and structure in adult rats with sustained hypertension. Twelve-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with the MR antagonist eplerenone (EPL, 100mg/kg/day) or placebo for 6 weeks. PenA function and structure were studied by pressure myography. Data are means±SEM at 60mmHg intralumenal pressure, placebo vs EPL. Myogenic tone generation was not different between groups (%myogenic tone: 40.3±2.3 vs 41.3±2.0). PenA diameter after tone was higher in EPL (42.47±1.5 vs 49.21±2.4μm, p=0.02, t-test). Dilation of PenA to nifedipine (calcium channel blocker) was improved after EPL treatment, as evidenced by an increase in diameter change (10μM nifedipine: 13.44±1.94 vs 18.44±2.39μm, p<0.01, Two-way ANOVA) and PenA diameter (10μM nifedipine: 58.01±2.28 vs 68.58±3.74μm, p<0.01, Two-way ANOVA). PenA passive structure was improved in SHRSP+EPL, as evidenced by an increase in PenA diameter (65.67±1.17 vs 81.00±5.11, p<0.01, Two-way ANOVA) and lumen diameter (55.17±1.8 vs 73.00±5.00, p<0.01, Two-way ANOVA), and a reduction in the wall-to-lumen ratio (0.10±0.01 vs 0.07±0.01, p<0.01, Two-way ANOVA). PenA stiffness was increased after EPL (β-coefficient: 10.91±0.93 vs 14.84±1.83, p=0.03, t-test), but distensibility was unchanged (24.45±3.20 vs 21.88±2.68). These data suggest that MR antagonism improves the structure of cerebral arterioles and their responsiveness to calcium channel blockade in adult rats with sustained hypertension. These improvements have the potential to reduce the risk of developing vascular cognitive impairments and dementia in chronically hypertensive subjects.