The stress-strain curves of mixtures of linear polyethylene and random ethylene-1-alkane copolymers have been studied. The molecular weights in each series were closely matched so that complications due to polydispersity and chain length differences were avoided. The pertinent variables were the composition, counit content, and crystallization mode. Comparison would be made of mixtures of the same molecular weight, depending on whether on whether or not cocrystallization took place. The characters of the stress-strain curves were found to be different for these two different situations. The small-deformation properties, such as the initial modulus and yield stress, were found to depend only on the total core crystallinity irrespective of crystallization mode and composition. On the other hand, ultimate properties such as the draw ratio break are very dependent on the phase structure of the system. In an important observation, which has other implications, it was found that crystallinity levels and ultimate properties were the same in the mixture and pure copolymers when comparison was made at the same nominal branch content.