PURPOSE: To investigate the effect of titanium dioxide (TiO) nanoparticles on the inhibition of the in vitro cellular activity of human Tenon's fibroblasts (HTFs) under UVA exposure. METHODS: The effects of TiO nanoparticles on human Tenon's fibroblasts were evaluated after 1, 4, 6, and 24 h of exposure to UVA at levels of 2.5, 5.0, and 10 J/cm. The methyl thiazolyl tetrazolium (MTT) assay was performed to measure the suppression of cellular metabolic activity. The lactate dehydrogenase (LDH) assay was performed to determine the extent of cell membrane damage. Flow cytometric analysis and inverted phase-contrast and electron microscopy were performed. The scratch wound assay was performed to visualize suppression of cellular migration. RESULTS: MTT assay values were similar between the UVA-exposed groups and the control group without UVA exposure. However, the combined exposure of TiO nanoparticles and UVA exposure induced significant dose-dependent inhibition of cellular viability and damage to HTFs, especially at concentrations of TiO equal to or greater than 100 μg/mL and 2.5 J/cm of UVA irradiation. Changes in cellular morphology increased in a dose-dependent pattern with a TiO concentration greater than 100 μg/mL under UVA exposure. At a TiO concentration of 150 μg/mL, damage to the cellular morphology of the HTFs was significantly increased, and nanoparticles were seen inside of the cytoplasm in the affected HTFs exposed to UVA. There was a significant reduction of cellular migration at TiO concentrations higher than 150 μg/mL. CONCLUSION: TiO nanoparticles inhibited the cellular activity of HTFs under UVA irradiation and showed potential for use to prevent the wound scarring of Tenon's fibroblasts. Further studies will be necessary to determine the optimal concentration of TiO nanoparticles and UVA exposure dose for clinical applications.