Abstract: Crystallization coexisting with crosslinking was obtained in novel phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) / copper phthalocyanine (CuPc) nanocomposites by in-situ crosslinking reaction. The PEN-Ph/CuPc nanocomposite films were prepared by pre-polymerization of PEN-Ph and 1,3,5-tri-(3,4-dicyanophenoxy) benzene (TPh) with the present of copper ion, followed by solution-casting and hot-compression methods. The influence of the crosslinking reaction and crystallization behaviour with different content of copper phthalocyanine as well as the changing of crystallization behaviour before and after hot compressing were investigated. The results show that the crystallization and crosslinking coexist in the system at the same time. Differential scanning calorimetry (DSC) analysis indicates that the degree of crosslinking increases with the increasing amount of copper ion, indicating that the copper ion can be used as a crosslinking agent in this system. The X-ray diffraction (XRD) result shows that crystallinity decreases slightly as the copper ion increases, owing to the effect of the restriction of the crystallization behavior by the crosslinking reaction. Scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns show that the crystals of the PEN-Ph matrix grow after the hot-compressing procedure. All of the results show that the crystallization and crosslinking can coexist in this system through in-situ compositing, and the hot-compressing is a useful method to improve the crystallization of the composites.