BACKGROUND/PURPOSE: Gut microbiota has been associated with liver cirrhosis and, possibly, hepatic encephalopathy. However, only a few studies have examined the link between mucosa-associated microbiota (MAM) and minimal hepatic encephalopathy (MHE). Our aim was to investigate this relationship. METHODS: Twenty-four patients with cirrhosis underwent colon biopsies at our institution, between January 2014 and April 2015. Patterns of microbial colonization were examined using 16S rRNA gene sequences. MHE was diagnosed using the Neuropsychological Test. RESULTS: Ten (41.7%) of the 24 patients were diagnosed as having MHE. There was no significant difference in the diversity of gut microbiota by sampling locations between those with and without MHE. However, the diversity of the gut microbiota and the proportion of the genus Bacteroides decreased as a function of declining liver function. We divided patients into those with the highest proportion of the genus Bacteroides (Bacteroides-dominant group; n = 9) and into a Bacteroides non-dominant group (n = 15). In the Bacteroides-dominant group, only 1 patient (11.1%) was diagnosed as having MHE, with the incidence rate of MHE being significantly lower in the Bacteroides-dominant group than in the non-dominant group (p = 0.019). The Child-Pugh score (p = 0.05) and use of proton-pump inhibitors (p = 0.015) were negatively correlated to the proportion of Bacteroides. Furthermore, the proportion of the family Clostridiaceae was significantly higher in the Bacteroides-dominant group than in the non-dominant group (p = 0.078). CONCLUSIONS: The decrease in microbial diversity and genus Bacteroides in MAM is a risk factor for MHE in patients with liver cirrhosis.