Hypothesis: Gut microbiota dysbiosis contributes to age-dependent hypertension (HTN) driven cognitive impairment (CI), which is attenuated by prebiotic dietary fiber supplementation. Methods: In 3 and 16 month (M) male Sprague Dawley rats, 3M rats receiving a fecal microbiota transplant (FMT) from 16M rats, and 16M rats fed a 6 week high prebiotic fiber (HPF) diet (n=4-6), BP, cognitive function (novel object recognition), hippocampal blood brain barrier (BBB) integrity (by FITC extravasation), gut microbiota taxonomy (by WGS) and short chain fatty acid (SCFA) levels (by GC-MS) were assessed. Results: Aged 16M rats exhibit gut microbiota dysbiosis, HTN, hippocampal BBB leakage and impaired cognition. FMT to 3M rats evoked gut microbiota dysbiosis (3M vs 3M + FMT: Cecal Bray-Curtis β diversity PCoA Species Bacteria, P=<0.05) and HTN. Linear Discriminant Analysis shows enrichment of cecal a) Lactobacillales (associated with lower BP) in 3M rats (LDA Log 10 4.69, P=0.022), b) Alistipes putrendenis in 16M rats (LDA Log 10 3.98, P=0.005), c) the Bacteroides genera (increased in HTN) in 3M + FMT rats (LDA Log 10 4.34, P=0.015). HPF attenuated gut microbiota dysbiosis (16M vs 16M + HPF: Fecal Bray-Curtis β Diversity PCoA Species Bacteria, P<0.05, PCoA MetaCyc, P<0.05; 16M pre vs post HPF: Fecal Bray-Curtis β Diversity PCoA Species Bacteria, P<0.05), increased SCFA levels, reduced BP and hippocampal BBB permeability and improved cognition. Conclusions: Gut microbiota dysbiosis contributes to age-dependent HTN-driven CI. HPF supplementation, a readily implementable lifestyle intervention, attenuates HTN driven CI via mechanisms independent of current antihypertensive medications.