Background/Aims: Preventing undesirable endothelial-mesenchymal transformation (EnMT) with repetitious in vitro expansion of human corneal endothelial cells (CECs) is a pivotal issue in cornea regeneration. Previous studies have shown that inhibition of the TGF-β pathway reduces epithelial-mesenchymal transformation. However, its potential role in EnMT remains poorly understood. As such, the effect of LY2109761, a novel TGF-β receptor type I and type II dual inhibitor, was investigated on EnMT. Methods: CECs cultured with various concentrations of LY2109761 were evaluated for their growth rate and phenotype. Additionally, the expression of functional markers (sodium-potassium pump Na+/K+-ATPase and the tight junction protein ZO-1) and mesenchymal markers (CD73, fibronectin, and vimentin) was detected using immunostaining and western blot. The mRNA expressions were also assayed by real-time polymerase chain reaction analysis. Results: At a 1 μM concentration, LY2109761 did not influence the proliferation of CECs and subsequent experiments were therefore performed using this concentration. Furthermore, CECs cultured in the presence of 1 μM LY2109761 maintained their ability to grow as a monolayer of hexagonal-shaped cells. The expression of functional markers increased in LY2109761-treated CECs, while the expression of mesenchymal markers decreased (both in protein and mRNA levels). Conclusion: Inhibition of TGF-β receptor type I and type II by LY2109761 maintained the phenotype of CECs and inhibited the EnMT process. These results indicate the possible continuous in vitro expansion of CECs with normal function.