Background: Barley, a grain rich in soluble dietary fiber β-glucan, is expected to lower blood pressure. Conversely, individual differences in its effects on the host might be an issue, and gut bacterial composition may be a determinant. Methods: Using data from a cross-sectional study, we examined whether the gut bacterial composition could explain the classification of a population with hypertension risks despite their high barley consumption. Participants with high barley intake and no occurrence of hypertension were defined as “responders” (n= 26), whereas participants with high barley intake and hypertension risks were defined as “non-responders” (n= 39). Results: 16S rRNA gene sequencing revealed that feces from the responders presented higher levels ofFaecalibacterium, Ruminococcaceae UCG-013,Lachnospira, andSubdoligranulumand lower levels ofLachnoclostridiumandPrevotella9 than that from non-responders. We further created a machine-learning responder classification model using random forest based on gut bacteria with an area under the curve value of 0.75 for estimating the effect of barley on the development of hypertension. Conclusions: Our findings establish a link between the gut bacteria characteristics and the predicted control of blood pressure provided by barley intake, thereby providing a framework for the future development of personalized dietary strategies.