AIM: To demonstrate the cytotoxic effect of betaxolol and its underlying mechanism on human corneal endothelial cells(HCE cells) in vitro and cat corneal endothelial cells(CCE cells) in vivo, providing experimental basis for safety anti-glaucoma drug usage in clinic of ophthalmology.METHODS: In vivo and in vitro experiments were conducted to explore whether and how betaxolol participates in corneal endothelial cell injury. The in vitro morphology, growth status, plasma membrane permeability, DNA fragmentation, and ultrastructure of HCE cells treated with 0.021875-0.28g/L betaxolol were examined by light microscope, 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, acridine orange (AO)/ethidium bromide (EB) double-fluorescent staining, DNA agarose gel electrophoresis, and transmission electron microscope (TEM). The in vivo density, morphology, and ultrastructure of CCE cells, corneal thickness, and eye pressure of cat eyes treated with 0.28g/L betaxolol were investigated by specular microscopy, applanation tonometer, alizarin red staining, scanning electron microscope (SEM), and TEM.RESULTS: Exposure to betaxolol at doses from 0.0875g/L to 2.8g/L induced morphological and ultrastructural changes of in vitro cultured HCE cells such as cytoplasmic vacuolation, cellular shrinkage, structural disorganization, chromatin condensation, and apoptotic body appearance. Simultaneously, betaxolol elevated plasma membrane permeability and induced DNA fragmentation of these cells in a dose-dependent manner in AO/EB staining. Furthermore, betaxolol at a dose of 2.8g/L also induced decrease of density of CCE cells in vivo, and non-hexagonal and shrunk apoptotic cells were also found in betaxolol-treated cat corneal endothelia.CONCLUSION: Betaxolol has significant cytotoxicity on HCE cells in vitro by inducing apoptosis of these cells, and induced apoptosis of CCE cells in vivo as well. The findings help provide new insight into the apoptosis-inducing effect of anti-glaucoma drugs in eye clinic.