Polyarylene ether nitrile (PEN) was synthesized via solution nucleophilic aromatic substitution polymerization with biphenyl (BP) and 2, 6-dichlorobenzonitrile (DCBN). PEN and randomly oriented multiwalled carbon nanotube (MWCNT)/PEN composite films were prepared by a solution casting method, then the as-prepared films were mono-axial hot-stretched at different ratios to enhance their degrees of orientation and crystallinity. Results showed that the thermal, crystalline, mechanical and dielectric properties of the PEN films were significantly enhanced after the hot-stretching process. When the films were hot-stretched at 200%, the melting points (Tms) of the films were ranged from 330.4 to 346.3 °C. Besides, the percentage of crystallinity of the composites increased from 4.92 to 19.16 %, the tensile strength of them increased from 121 to 451 MPa and the dielectric constant of them also increased from 4.0 to 6.7 (1 kHz). Moreover, the electrical properties of MWCNT/PEN composite films during the hot-stretching procedure were studied. When the amount of MWCNT was close to the percolation threshold (ca. 6 wt%), the dielectric properties, electrical conductivity and energy density were proved to be influenced by the stretch ratios. The electrical conductivity of composites increased from 5.2 × 10-5 S cm-1 to 1.6 × 10-4 S cm-1 (1 kHz), the dielectric constant of composites increased significantly from 378.0 to 1298.1 (100 Hz) and the energy density of the composites increased from 2.51 to 3.50 J cm-3 at 50% stretch ratio. All results showed that the crystalline, mechanical, thermal and dielectric properties of PEN based composite films could be enhanced by hot-stretching.