Cocrystallization and phase segregation phenomena of polyethylene (PE) blends between the deuterated and hydrogenous species with various degrees of branching were investigated as a function of the D/H blend content on the basis of the measurements of DSC and temperature dependence of FTIR spectra. For the blend samples between the deuterated high-density PE (DHDPE) and the hydrogenous linear low-density PE [LLDPE(2), branching content ca. 17 ethyl groups/1000 carbons] the almost perfect cocrystallization phenomenon was found to occur for all the samples with different blend contents from 0 to 100% even when cooled slowly from the molten state to room temperature. The blends of DHDPE with LLDPE(3) (branching content ca. 41 ethyl groups/1000 carbons) or HDPE (ca. 1 branching/1000 carbons) were found to show basically the phase segregation phenomenon between the D and H species but partly the cocrystallization was also found to occur when the dilution of the D or H component was high. A concrete relationship between the degree of cocrystallization and the branching and D/H content was discussed on the basis of infrared band profile analysis.