The purpose of this study is to determine a structural explanation for the improved ability of PBT for biaxial orientation at the temperature range of $100{sim}180^{circ}C$. In order to investigate the crystal structure and orientation, PBT films with biaxial and uniaxial stretching are examined using WAXD, MOA, etc. Thermal properties are confirmed by DMTA, DSC and mechanical properties are investigated using sonic propagation method and tensile tester. In WAXD results, original PBT films exhibit only ${alpha}$-form crystallites, while biaxially stretched films show (100) of the ${alpha}$-crystal phase with increased stretching temperatures. In MOA patterns, original and biaxially stretched PBT films show an isotropic pattern in the film plane. The planarity of the film increases with simultaneous transverse stretching and stretching temperature.