To determine the relationship of thick greasy tongue fur formation and permeability of vascular endothelial cells (ECs) with the protein expression of zonula occludens-1 (ZO-1). Sprague Dawley rats were randomly divided into a model group of severe acute pancreatitis (SAP) and a sham-operated (SO) group. The SAP rats were further divided into two subgroups on the basis of tongue-coating status: a thick greasy tongue fur group (SAP-TGF) and a normal tongue fur group (SAP-NF). Six rats were chosen randomly from every group mentioned above for an Evans blue assay 5 days after model establishment. For the histomorphology analysis, the expressions of ZO-1 protein and mRNA were studied by hematoxylin-eosin (H&E) staining, transmission electron microscope, Western blot, and Q-PCR using blood and tongue tissues, which were collected from 8 rats randomly chosen from each group. The papillae density of the rat tongue surface and the caryocinesis frequency of the basal layer were significantly increased in the SAP-TGF group compared with the SO group (P < 0.05). Evans blue levels in the tongue tissue of the SAP-TGF group were significantly higher than that of the SO and SAP-NF groups (P < 0.05). Vascular ECs were wider and obviously fissured in the SAP-TGF group under transmission electron microscope observation. The protein and mRNA expression of ZO-1 in the SAP-TGF group were lower than those in the SAP-NF (P < 0.05). Reproductive activity enhancement of glossal epithelial cells was one of the main characteristics of thick greasy tongue fur formation. An increase in vasopermeability was closely associated with thick greasy tongue fur formation. Tight junction structural variation of vascular ECs might play an important role in the pathological and physiological process of thick greasy tongue fur formation.