Lymphangiogenesis is induced by various growth factors, including VEGF-C. Although TGF-beta plays crucial roles in angiogenesis, the roles of TGF-beta signaling in lymphangiogenesis are unknown. We show here that TGF-beta transduced signals in human dermal lymphatic microvascular endothelial cells (HDLECs) and inhibited the proliferation, cord formation, and migration toward VEGF-C of HDLECs. Expression of lymphatic endothelial cell (LEC) markers, including LYVE-1 and Prox1 in HDLECs, as well as early lymph vessel development in mouse embryonic stem cells in the presence of VEGF-A and C, were repressed by TGF-beta but were induced by TGF-beta type I receptor (T beta R-I) inhibitor. Moreover, inhibition of endogenous TGF-beta signaling by T beta R-I inhibitor accelerated lymphangiogenesis in a mouse model of chronic peritonitis. Lymphanglogenesis was also induced by T beta R-I inhibitor in the presence of VEGF-C in pancreatic adenocarcinoma xenograft models inoculated in nude mice. These findings suggest that TGF-beta transduces signals in LECs and plays an important role in the regulation of lymphangiogenesis in vivo.