The structure change in spherulites for hydrostatically extruded polypropylene (PP) was studied by the use of internal friction measurements and thermophotometry tests. The onset temperature of the beta-loss peak of the PP sample decreases with increasing reduction in area, R. For the extrudates below R = 50%, the peak temperature of a-loss shifts to lower temperature. The alpha and beta absorptions for the extrudates up to R = 50% become broad and overlap with each other. The intensity of the beta-loss peak, Delta(max), is maximum for the extrudate with R = 50%. The results of tan delta, damping, and the intensity of the beta-loss peak indicate that the mechanism of molecular chain deformation is divided into two stages, below and above R = 50%. The results are due to spherulitic changes, i.e. the shape of spherulites changed from spherical to elliptical in the extrudates above R = 50% and the spherulite with R = 50% changed from coarse structure to a finer one by the imposition of hydrostatic pressure.