Endothelial-mesenchymal transition (EndMT) is closely associated with embryogenesis, injury restitution, tissue neogenesis, tumor progressions and viscera fibrosis. EndMT may occur in the proximal tubular endothelial cells, inducing fibroblasts to produce matrix and then accelerating the process of cardiac fibrosis. Transforming growth factor-β1 (TGF-β1), a profibrotic cytokine, was recently shown to be a crucial trigger of EndMT in tubular endothelial cells. Increasing evidence suggests that growth factor receptor-bound 2 (GRB2) dysfunction affects fibrocytes; thus, GRB2 may be a novel target for treating fibrosis. The miR-200 miRNA cluster (miR-429, miR-141, miR-200c, miR-200b and miR-200a) was reported to inhibit EndMT. However, the underlying mechanisms, specifically that of miR-200a, are unclear. To elucidate the vital role of miR-200a in EndMT, we established a cardiac interstitial fibrosis model with a widely used EndMT assay, TGF-β1-induced EndMT in human aortic endothelial cells (HAECs). We found that overexpression of miR-200a blocked EndMT in HAECs by inhibiting fibroblast-specific protein-1 (FSP-1) and α-smooth muscle actin (α-SMA) expression and increasing platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial cadherin (VE-cadherin) expression, regardless of the presence of TGF-β1. MiR-200a expression was suppressed during the EndMT process, in both time- and dose-dependent manners, following GRB2 upregulation. EndMT was promoted by ectopic expression of GRB2 via decreased CD31 and VE-cadherin. Furthermore, EndMT was partially inhibited by co-transfection of miR-200a with GRB2 ORF, likely by restoring CD31 and VE-cadherin expression. MiR-200a negatively regulated GRB2 protein levels via direct binding to the GRB2 3′UTR. Finally, these discoveries may provide novel insights into the functional mechanism of miR-200a in regulating fibrosis via the TGFβ1/miR-200a/GRB2/EndMT pathway, and miR-200a may serve as a new target for treating fibrosis in the future.