In this study, the authors employed a good dispersion of multiwalled carbon nanotubes (MWCNTs) within the phase change material (PCM)/polymer (polyethylene glycol/polyacrylonitrile) electrospinning solution to enhance the thermal properties of shape-stabilized phase change nanocomposite nanofibers (SPCNNs). In this regard, nanofibers with and without MWCNTs were produced (with approximately similar diameters), and the effect of a good dispersion of MWCNTs on the thermal, physical, and mechanical properties of the nanofibrous samples was evaluated. Scanning electron microscopy and transmission electron microscopy were utilized to observe the surface morphology and interior structures of electrospun nanofibers, respectively. Differential scanning calorimeter (DSC) and thermogravimetric analysis were utilized to evaluate the degree of crystallinity (DOC) and thermal stability of the samples, respectively. The DSC results of phase change nanofibers (PCNs) and the phase change nanocomposite nanofibers (PCNNs) confirmed that the presence of MWCNTs extremely boosts the DOC of nanofibers (44.69% and 93.64% for PCNs and PCNNs, respectively), which can be attributed to the nucleation effect of MWCNTs. Moreover, the X-ray diffraction pattern and tensile test results showed that the presence of MWCNTs can affect the average size of crystals and mechanical strength of nanofibers, respectively. Altogether, the present study demonstrates that the SPCNNs have good mechanical and thermal properties and appropriate potential for use in numerous thermal energy storage applications.