The effects of nanoparticle concentration and processing conditions on the relaxation behavior of PEN nanocomposites are investigated using mechano optical techniques where birefringence, true stress and true strain are measured while subjecting the polymer films to uniaxial deformation followed by relaxation. For this purpose, two different stretching temperatures were employed to stretch the films containing 0.5 and 2 wt % nanoparticles: one above and the other below the T-parallel to (liquid-liquid transition). Increasing the temperature as well as the addition of nanoparticles suppresses the spontaneous deformation processes leading to sharp increase in true strain. An instantaneous stress drop is observed during relaxation below the T-parallel to corresponding to the initial glassy component observed in the stress-optical behavior during stretching. This stress is attributed to the presence of segmental rigid correlations that were not broken during the stretching stage. This behavior was found to be absent above the liquid-liquid transition as they are already melted. Nanoparticles were found to act as suppressors of crystallinity during stretching. Their presence reduces likelihood of strain crystallization as they reduce the relaxation of oriented chains into favorable registry with each other to crystallize. During relaxation, the presence of nanoparticles was found to increase the crystallinity. Their presence increases the population of oriented amorphous chains during deformation that relax into favorable registry with each other leading to increase in crystallinity.