The characteristic features of chronic peritoneal injury with peritoneal dialysis (PD) are submesothelial fibrosis and neoangiogenesis. Transforming growth factor (TGF)-β and vascular endothelial growth factor (VEGF)-A are the main mediators of fibrosis and neoangiogenesis, respectively; however, the effect of the interaction between them on the peritoneum is not well known. In this study, we investigated the relationship between TGF-β1 and VEGF-A in inducing peritoneal fibrosis using human tissues and dialysate, cultured cells, and animal models. The VEGF-A concentration correlated with the dialysate-to-plasma ratio of creatinine (D/P Cr) (P<0.001) and TGF-β1 (P<0.001) in human PD effluent. VEGF-A mRNA levels increased significantly in the peritoneal tissues of human ultrafiltration failure (UFF) patients, and correlated with number of vessels (P<0.01) and peritoneal thickness (P<0.001). TGF-β1 increased VEGF-A production in human mesothelial cell-lines and fibroblast cell-lines, and TGF-β1-induced VEGF-A was suppressed by TGF-β receptor I (TGFβR-I) inhibitor. Incremental peak values of VEGF-A mRNA stimulated by TGF-β1 in human cultured mesothelial cells derived from PD patients with a range of peritoneal membrane functions correlated with D/P Cr (P<0.05). To evaluate the regulatory mechanisms of VEGF-A and neoangiogenesis in vivo, we administered TGFβR-I inhibitor intraperitoneally in a rat chlorhexidine-induced peritoneal injury (CG) model. TGFβR-I inhibitor administration in the CG model decreased peritoneal thickness (P<0.001), the number of vessels (P<0.001), and VEGF-A levels (P<0.05). These results suggest that neoangiogenesis is associated with fibrosis through the TGF-β1-VEGF-A pathway in mesothelial cells and fibroblasts. These findings are important when considering the strategy for management of UFF in PD patients.