Orientational behaviours of syndiotactic 1, 2 poly-butadiene samples with different crystallinity have been studied. The birefringences of the uniaxially stretched samples show negative values, and the absolute values increase when the samples are released. Crystal orientations in the stretched and released samples were examined by the X-ray diffraction method. The intrinsic birefringence in the crystalline phase was estimated as -63.2×10-3 using the bond polarizability proposed by Bunn and Vulk. Consideration about amorphous contribution to the birefringence based on the additive assumption led to a conclusion that the conformation of the structural unit in amorphous phase must change from perpendicular to parallel structure during the stretching process.