With the rapid development of Nano technology, the apply of nano - TiO2 has become wider and wider in both technology and social life . It has brought convenience in life. At the same time, its potential toxicity, caused by the physical and chemical transformation of its property, has received more and more concern. This article, from the prospect of in vitro and in vivo level, not only gives a brief introduction of the development of research on toxicity of nano - TiO2, but also expounds its potential bioeffect on human and other living organisms, and the necessity of new safety assessment on nano - TiO2.