The effect of Al2O3 and MCNT nanoparticles on the crystallization behaviors, subsequent melting phenomenon, microstructures and mechanical performances of PEEN-based nanocomposites was first investigated and reported. It was found that the absence of nucleating role of Al2O3 made PEEN / Al2O3 nanocomposites show similar melting/cold crystallization and corresponding melting behaviors as those of PEEN matrix. By contrast, MCNT could play two different and competing roles in the crystallization process: acting as nucleating agents and constraining the mobility of polymer chains to hinder crystal growth. Consequently, PEEN/MCNT nanocomposites exhibit the increased T-c' but the decreased W-c' and double T(m)s. Heat treatment at 220 degrees C for 2 h turned to be an effective way to finish the cold crystallization process for PEEN and their nanocomposites. SEM images showed that spherical crystallite clusters could be clearly observed in PEEN and PEEN/Al2O3 nanocomposite, which were in well agreement with the DSC and WXRD results. The higher W-c of PEEN/Al2O3 nanocomposites also led to better impact and flexural strength than those of PEEN/MCNT nanocomposite. This research is expected to help us understand the crystallization behaviors and final properties of PEEN-based materials influenced with these two different dimensional nanoparticles.