Well-aligned poly(azo-naphthyl-imide) (PANI) fibers and PANI/multi-walled carbon nanotube (MWCNT) nanofibers-based nanocomposite were produced via self-reinforcement. High-molecular-weight 31 x 10³ g mol^-1 PANI has been fabricated in this study. Scanning electron microscopy and transmission electron microscopy showed that the electrospun PANI/MWCNT nanofibers were uniformly aligned and almost free of defects. The as-prepared well-aligned electrospun nanofibers were then utilized as homogeneous reinforcement to enhance the tensile strength and toughness of films. Compared with neat 3 wt% PANI nanofibers (304.6 MPa), the tensile strength for the film reinforced with 3 wt% PANI/MWCNT nanofibers (245.9 MPa) was considerably increased. The significant enhancement in the overall tensile properties of the PANI/MWCNT nanofibers-reinforced polyimide films was ascribed to good compatibility between the electrospun nanofibers and the matrix as well as high nanofiber orientation in the matrix. The thermal stability of PANI/MWCNT nanofibers-reinforced polyimide was also superior having 10% gravimetric loss of 599–625°C and glass transition temperature of 243–261 °C relative to the neat polymer and PANI nanofiber-based system. High-performance polyimide nanocomposites via self-reinforcement can act as potential contenders for light-weight aerospace materials.