Abstract: Bacterial cellulose (BC)/TiO2 composite membranes with porous, polar and good thermal stability as novel separator for lithium ion battery were prepared by using TiO2 nanoparticles prepared by sol-gel method to mix with BC nanofibers. The pore structure, lyophilic performance, thermal stability, electrochemical stability, ionic conductivity and battery cycling stability of the composite membranes were characterized by a variety of techniques. The research results indicated that BC/TiO2 composite membranes have a three-dimensional porous structure, good electrolyte absorptivity and dimensional stability at high temperature. Compared to the commercial membrane (Celgard?2325), BC/TiO2 composite separators have higher ionic conductivity. With the increase of TiO2 nanoparticles content, the ionic conductivity increased at first and decreased subsequently. When the content of TiO2 nanoparticles is 20.81 %, the BC/TiO2 composite separator has the highest ionic conductivity (1.7010-3S/cm). When used the composite membranes as the separators for lithium ion battery, the battery shows its good cyclic stability and high rate discharge performance. This research has a guiding significance in the preparation of lithium ion battery separator with excellent thermal stability and ionic conductivity.