The mechanical, thermal, and fracture morphological characterization of low-density polyethylene (LDPE) composites reinforced with vapor-grown carbon nanofibers (VGCNFs) is presented in this article. VGCNF/LDPE composites with different VGCNF weight percentages were prepared by single-screw extrusion followed by injection molding. Scanning electron microscopy showed that VGCNFs were predominantly dispersed uniformly within the LDPE matrix. Differential scanning calorimetry has shown that the VGCNF/LDPE composites crystallized at higher temperatures than pure LDPE polymer. Tensile testing has shown that strength and Young's modulus of VGCNF/LDPE composites were improved by 15% and 44%, respectively, when the VGCNF loading reached 3 wt%.