Nano alumina, one of the most important nanomaterials, is widely used in diverse areas. It was reported that nano alumina could cross the blood brain barrier to enter the brain. Considering aluminum accumulation in brain is closely related to many neural diseases. We studied the neural toxicity of four nano gamma-alumina samples by using neural stem cells (NSCs) C17.2 as a model. We find that the toxicity of nano gamma-alumina is pretty low, though these alumina particles are easily internalized by cells. The loss of cell viability and membrane integrity are dose-dependent and sample-dependent after alumina exposure. At concentrations lower than 100 microg/mL, no significant toxicity is observed for all alumina samples. When the concentration reaches 200 microg/mL, alumina treated cells begin to loss their activities. No culture period effect (up to 3 days) is observed. Very tiny soluble aluminum and the absorption of culture medium ingredients onto alumina particles do not affect the cell viability. Intracellular reactive oxygen species generation may contribute to the cytotoxicity of alumina particles at high concentration, but it does not induce the apoptosis of NSCs.