Abstract: TiO₂ / ( PEO)₈LiClO₄ composite polymer elect rolyte films were prepared by a solution cast method. TiO₂particles were in2si tu formed in ( PEO)₈LiClO₄ mat rix by simply mixing PEO , LiClO₄ and tet rabutyl titanate andthen drying. The morphology , thermal performance and conductivity of the films were studied using SEM , DSC andelect rical impedance spect roscopy , respectively. The result s show that the in-situ formed TiO₂ particles are founduniformly dispersed in PEO mat rix. The glass t ransition temperature and crystallinity of the films are lowered due tothe presence of TiO₂ . The conductive behaviour of the films follows an Arrhenius type relation. A maximal conductivity 5. 5 ×10 - 5 S/ cm at 20 ℃of the TiO₂ / ( PEO)₈LiClO₄ film was obtained at 5 % mass f raction of TiO₂ . Thepolymer lithium ion battery with the elect rolyte films exhibit s stable discharge voltage. The discharge specificcapacity could still retain 107 mAh/ g af ter 20 cycles.