Objective <p>Rho guanine nucleotide exchange factor 15 (ARHGEF15) is a member of the RhoGEF family that activates the Rho protein. High ARHGEF15 expression is associated with poor prognosis in patients with pancreatic cancer. Although ARHGEF15 is abundantly expressed in endothelial cells, its detailed functions remain unknown. This study aimed to elucidate the effects of ARHGEF15 on endothelial cells and the underlying molecular mechanisms involved.</p> Methods <p>The <i>ARHGEF15</i> gene was overexpressed or knocked down in human umbilical vein endothelial cells (HUVECs), and the results were validated via qRT-PCR and Western blotting. CCK8 and MTT assays were used to evaluate cell proliferation. Wound healing and transwell assays were used to assess cell migration. The activation of STAT3 signaling was examined by Western blotting, and STATTIC was used to inhibit STAT3 signaling.</p> Results <p>ARHGEF15 overexpression promoted the migration of HUVECs, and ARHGEF15 knockdown inhibited the migration of HUVECs. Neither the overexpression nor the knockdown of ARHGEF15 affected HUVEC proliferation.</p> <p>Furthermore, ARHGEF15 increased STAT3 phosphorylation in HUVECs. STATTIC treatment prevents ARHGEF15 overexpression-induced STAT3 phosphorylation and HUVEC migration.</p> Conclusion <p>ARHGEF15 increases HUVEC migration by regulating STAT3 signaling.</p>