The crystalline structures associated with melting and crystallization behaviors of monodisperse linear polyethylene confined in cylindrical nanopores were investigated by X-ray diffraction and differential scanning calorimetry. The crystalline structures, melting, and crystallization behaviors of PE under the imposed cylindrical confinement were noticeably different from those of the bulk state. The isothermal crystallization experiments showed that the overall crystallization of polyethylene in cylindrical nanopores was dominated by the nucleation rather than the growth of crystallites. The c- and a-axes of orthorhombic PE crystals developed in nanoporous alumina were preferentially oriented perpendicular to the long axis of cylindrical nanopore while the b-axis was parallel to the pore axis. The melting temperature of polyethylene in the nanopores was substantially depressed, and it was analyzed with the Thomson-Gibbs equation. The crystallinity of linear polyethylene in cylindrical nanopores was less than 50%, whereas the bulk value was 71.6%.