The tensile deformation and fracture behavior of commercially available low-density polyethylene (LDPE) films, having different molecular characteristics, was studied. Submitting samples to specific thermal histories controlled the morphological structure of these semicrystalline polymers. Phase-structure analysis of the resulting materials was performed by DMA and DSC analyses. The plane-stress essential work of fracture methodology was chosen because the materials used had failed after complete necking of the remaining ligament. Significant differences in behavior, induced by thermal treatments, were found for the tensile yield stress and the specific nonessential work of fracture, but not in the specific essential work of fracture. The results show that the mechanical properties and fracture behavior depend not only on the crystallinity levels and molecular weight characteristics of the samples, but also upon the degree of structural continuity. The beta-relaxation process, associated with the crystal-amorphous interphase, strongly influences the fracture behavior at testing temperatures chosen below the beta-relaxation temperature.