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Background: Angiogenesis and vascular dysfunction play important roles in the occurrence and development of Crohn's disease (CD), but relevant mechanistic research is lacking. This paper aimed to use exosomal technology to elucidate the mechanism of vascular abnormalities in CD.Methods: Ultra-high-speed centrifugation was used to extract circulating exosomes. Electron microscopy, particle size, and biomarker detection were used for exome quality control. MicroRNA 21 (miR-21) levels were determined by quantitative polymerase chain reaction (qPCR). Migration abilities and tubule-forming capacity were assessed by wound healing assay, transwell invasion test, and tube formation assay. Exosome biomarkers and pathway protein levels were determined by western blotting.Results: Our data revealed that the circulating exosomes of patients with CD have a remarkable effect on the proliferation and migration of human umbilical vein endothelial cells (HUVECs), and that exosomal miR-21 levels were highly elevated in exosomes derived from the plasma of CD patients. Exosomes derived from CD patients and miR-21 mimic had more powerful migration abilities and tubule-forming capacity than control groups. miR-21 inhibitors significantly blocked the quick migration and tubule formation of HUVECs induced by CD-exosomes. Western blot analysis revealed that circulating exosome miR-21 in HUVECs might weaken negative regulation of phosphoinositide 3-kinase (PI3K)/AKT serine/threonine kinase (AKT) by target-inhibiting phosphatase and tensin homolog (PTEN) and inducing the expression of hypoxia-inducible factor 1-alpha (HIF-1α) and vascular endothelial growth factor (VEGF).Conclusions: Circulating exosomal miR-21 mediates HUVEC proliferation and migration through PTEN/PI3K/AKT in CD. Exosomal miR-21 may be a new biomarker or therapeutic target for the treatment of vascular abnormalities in CD.