Aim: To investigate the primary mechanism of photoexcited TiO2 nanoparticles -induced apoptosis in Bel-7402 cell. Methods: Bel-7402 cells were treated with photoexcited TiO2 nanoparticles. Cells inhibitory rate was assayed by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) method. Cell apoptosis was evaluated by both flow cytometry (FCM) and Haematoxylin and Eosin (HE) Staining method. Expression of caspase 3 and bcl-2 were determined by Western blot, respectively. Results: Photoexcited TiO2 nanoparticles exhibited good inhibition effects on Bel-7402 cells under appropriate TiO2 concentration; Both morphological observations and FCM results showed that photoexcited TiO2 nanoparticles induced apoptosis in Bel-7402 cells with concomitant increase of activated caspase-3 expression and decrease of bcl-2 expression. Conclusion: Photoexcited TiO2 nanoparticles can apparently inhibit Bel-7402 cells under appropriate concentration, and the inhibition process follows first order reaction rule approximately. In addition, photoexcited TiO2 nanoparticles can remarkably induce apoptosis in Bel-7402 cells, and the molecular mechanism of apoptosis is closely associated with increase of activated caspase-3 and down-regulation of the bcl-2 expression. The present work provides strong experimental foundation of Photoexcited TiO2 nanoparticles in the clinical treatment of tumor.