Stem cells have been the subject of increasing scientific interest because of their utility in numerous biomedical applications. Stem cells are capable of renewing themselves; that is, they can be continuously cultured in an undifferentiated state, giving rise to more specialized cells of the human body. Therefore, stem cells are an important new tools for developing unique, in vitro model systems to test drugs and chemicals and a potential to predict or anticipate toxicity in humans. In the present study, in vitro cultured F3 immortalized human neural stem cell line and in vivo adult Sprague Dawley rats was used to evaluate the cytotoxicity of anticancer drug paclitaxel. In vitro apoptotic activity of paclitaxel was evaluated in F3 cell line by a MTT assay and DAPI test. The cell death was induced with the treatment of 20 nM paclitaxel and chromatin degradation was detected by DAPI staining, which was analyzed by fluorescent microscope. In vivo studies, we also observed nestin immunoreactivity on subventricular zone, which is stem cell rich region in the adult brain of the SD rat. Immunofluorescent staining result shows that pixel intensities of nestin were decreased in a dose dependent manner. These results suggest that paclitaxel is able to induce cytotoxic activity both in F3 neural stem cell line and neural stem cell in SD rat brain.