The morphology and molecular mobility of polyethylene were investigated by X-ray diffraction and C-13 solid-state NMR as a function of temperature. The test specimens chosen are melt films, single-crystal mats, undrawn dry gel films, and ultradrawn films with a draw ratio of 300. The semilogarithmic plot of the C-13 magnetization of the peak height of the line at 33 ppm indicated the existence of three different kinds of spin-lattice relaxation time (T-1C) : a slow decay time, an intermediate decay time, and a rapid decay time for the orthorhombic crystal form. Among the test specimens, the decay time of the ultradrawn gel film was the longest. The spin-spin relaxation time (T-2C) indicated that the noncrystalline component consists of an interfacial region and a rubber-like amorphous region with extensive molecular mobility. For single-crystal mats and dry gel films, the length of the interfacial region calculated using both the mass fraction of the interfacial region by C-13 NMR and the long period by X-ray scattering was almost equal to the length of the interfacial region estimated by analyzing a systematic deviation of the X-ray scattering curves at large angle tail from Pored’s law. Furthermore, the crystallinity at room temperature estimated by C-13 NMR was also in good agreement with the results by density and X-ray diffraction. With increasing temperature, Tie for the crystalline region became shorter, while T-2C for the noncrystalline region became longer, indicating more active molecular mobility. The crystallinity estimated by C-13 NMR was confirmed to decreased with increasing temperature. This tendency was in good agreement with the results obtained by X-ray diffraction using Ruland’s method;