The thermal expansion of (hk0) lattice spacing of quenched crystal and (040) and (110) lattice spacings of monoclinic crystal, as well as the orientation behavior of crystalline and non-crystalline phases of quenched, semi-annealed and well-annealed specimens of isotactic polypropylene with uniaxial stretching at various temperature, were investigated by means of simultaneous measurements of x-ray diffraction and birefringence.Abrupt change of thermal expansion coefficient of the crystal lattice spacings was found at 48 and 115°C for the quenched and monoclinic crystals, respectively. The former temperature may correspond to the beginning of melting of the quenched crystal, because of unusual value of the coefficient as large as 10×10-4deg-1 for the (hk0) lattice spacing beyond the temperature, while the latter corresponds to a sort of crystal disordering temperature of the monoclinic crystal.For the quenched specimen, the orientation of the quenched crystal (c-axis) and non-crystalline chain segment proceed more prominently at 20°C. than 50 °C. This inferior orientation at 50°C. may be interpreted in terms of partial melting of the quenched crystal, which gives less effective orienation of the crystal and non-crystalline chain segment during stretching. Crystal conversion from quenched to monoclinic system is found for the high-temperature stretching.For the annealed specimens, the orientation behavior of a′- and b- axis of monoclinic crystal, in which the negative orientation of a′-axis is always behind that of b-axis at relatively low degree of stretching and coincide with each other at a relatively high degree of stretching, is quite similar to that of b- and a-axis of polyethylene. This behavior may be interpreted in terms of deformation mechanism of polymer spherulite and disintegration of spherulite texture to the fibre. Upon comparing the orientation behavior at 20°C. with that at 120°C. the negative orienttation of b- and a′-axes proceed more prominently at 20°C, than at 120°C. at relatively low degree of streching, and vice versa at higher degree of stretching. This temperaturee sensitive behavior, especially at the relatively low degree of stretching, is also very similar to that of polyethylene, and may be interpreted in terms of the easiness of crystal slippage along (040) plane due to the abrupt change of interaction betweeen the crystal planes at the crystal disordering temperature.