The short-chain fatty acid (SCFA) butyric acid maintains a healthy gut barrier and vascular endothelium. We aimed to investigate the association between fecal butyric acid, carotid atherosclerosis and risk factors for ischemic stroke. Patients with severe carotid atherosclerosis (i.e. ≥ 50% stenosis) (n = 43) were compared with healthy controls (n = 38). We analyzed fecal SCFAs by gas chromatography, microbiota composition by 16S rRNA sequencing, markers of gut barrier damage and inflammasome activation by immunoassay, and plasma SCFAs by ultra-high performance liquid chromatography-tandem mass spectroscopy. Patients had higher fecal butyric acid level (p = 0.024), along with increased functional potential of microbial butyric acid production (p = 0.031), compared with controls. Dietary fiber intake was comparable. Patients had higher levels of gut barrier damage markers CCL25 and IFABP, and the inflammasome activation marker IL-18, whereas plasma level of butyric was similar. Increased fecal butyric acid was associated with higher BMI, waist-hip ratio, HbA1c, CRP and leukocyte count. Contrary to our hypothesis, patients with severe carotid atherosclerosis had higher fecal butyric acid level, and increased microbial production, compared with controls. Gut barrier damage in patients might indicate decreased absorption of butyric acid and hence contribute to the higher fecal level.