The nanosized titanium dioxide (nano-TiO2) is produced abundantly and used widely in the chemical, electrical/electronic and energy industries because of its special photovoltaic and photocatalytic activities. Past reports have shown that the nano-TiO2 can enter into the human body through different routes such as inhalation, ingestion, dermal penetration and injection. The effects of nano-TiO2 on different organs are currently being investigated and the concerns on its large scale applications such as sunscreen, etc. indeed become more interesting for us to investigate and to find the possible right answers for right doses for a safer application. In this research, the cytotoxicity of the nano-TiO2 was investigated in PC12 cells, a cell line used as a model in vitro for the brain neurons research. While the PC12 cells were treated with different concentrations of nano-TiO2 (1, 10, 50 and 100 microg/ml), the viability of cells was significantly decreased in the periods of 6, 12, 24 and 48 h, showing a significant dose effect and time-dependent manner. Meanwhile, the flow cytometric assay gave indication that the nano-TiO2 induced intracellular accumulation of reactive oxygen species (ROS) and the apoptosis of PC12 cells with the increasing concentration of nano-TiO2. Interestingly, pretreatment of N-(mercaptopropionyl)-glycine (N-MPG), known as a type of ROS scavenger formulations, could somehow inhibit PC12 apoptosis induced by the nano-TiO2. These results might have revealed a key mechanism in PC12 apoptosis under the effect of the nano-TiO2 solutions.