The structure of polyethylene (PE) blends between deuterated high-density PE (DHDPE) and hydrogeneous PE with various degrees of side chain branching (for example, linear low-density PE (LLDPE)) has been investigated on the basis of wide-angle and small-angle X-ray scatterings, infrared absorption spectra, and small-angle light scattering measured at room temperature. For the blend samples showing an almost perfect cocrystallization phenomenon between the D and H species (DHDPE + LLDPE-(2)), the unit cell parameters, crystallite size, interlamellar spacing, and spherulite size change continuously depending on the relative D/H content. For the case showing phase segregation between the D and H species (DHDPE + LLDPE(3)), lamellae consisting of either D or H chains are stacked together to form a spherulite, the size of which is remarkably larger than those of the pure D or H component.