The heterodimeric integrin receptor α4β7 regulates CD4 T cell recruitment to inflamed tissues, but its role in the pathogenesis of nonalcoholic steatohepatitis (NASH) is unknown. Here we examined the role of α4β7-mediated recruitment of CD4 T cells to the intestine and liver in NASH.Male littermate F11r+/+ (control) and junctional adhesion molecule A knockout F11r-/- mice were fed a normal diet or a Western diet (WD) for eight weeks. Liver and intestinal tissues were analyzed by histology, qRT-PCR, 16s rRNA sequencing and flow cytometry. Colonic mucosa-associated microbiota was analyzed using 16s rRNA sequencing. Liver biopsies from NASH patients were analyzed by confocal imaging and qRT-PCR.WD-fed knockout mice developed NASH and had increased hepatic and intestinal α4β7+ CD4 T cells relative to control mice which developed mild hepatic steatosis. The increase in α4β7+ CD4 T cells was associated with markedly higher expression of the α4β7 ligand mucosal addressin cell adhesion molecule 1 (MAdCAM-1) in the colonic mucosa and livers of WD-fed knockout mice. Elevated MAdCAM-1 expression correlated with increased mucosa-associated Proteobacteria in the WD-fed knockout mice. Antibiotics reduced MAdCAM-1 expression indicating that the diet-altered microbiota promoted colonic and hepatic MAdCAM-1 expression. α4β7 blockade in WD-fed knockout mice significantly decreased α4β7+ CD4 T cell recruitment to the intestine and liver, attenuated hepatic inflammation and fibrosis, and improved metabolic indices. MAdCAM-1 blockade also reduced hepatic inflammation and fibrosis in WD-fed knockout mice. Hepatic MAdCAM-1 expression was elevated in NASH patients and correlated with higher expression of α4 and β7 integrins.These findings establish α4β7/MAdCAM-1 as a critical axis regulating NASH development through colonic and hepatic CD4 T cell recruitment.Nonalcoholic steatohepatitis (NASH) is an advanced and progressive form of nonalcoholic fatty liver disease (NAFLD), and despite its growing incidence no therapies currently exist to halt NAFLD progression. Here, we show that blocking integrin receptor α4β7-mediated recruitment of CD4 T cells to the intestine and liver not only attenuates hepatic inflammation and fibrosis, but also improves metabolic derangements associated with NASH. These findings provide evidence for potential therapeutic application of α4β7 antibody in the treatment of human NASH.