Cocrystallization phenomenon between the hydrogenous (H) and deuterated (D) species of a series of isotactic polypropylene blends with various D/H contents has been established for the first time on the basis of the detailed analysis of thermal and infrared spectral data for both alpha 1 and alpha 2 crystalline forms, where the alpha 1 form is the crystal form of disordered chain packing mode but the alpha 2 form has the ordered chain packing structure. The melting point has been found to shift continuously towards higher temperature side with an increase in the H component. This continuous change in the melting and crystallization point was reasonably interpreted by assuming the coexistence of D and H chain stems in the crystal lattice. The so-called correlation splitting was detected as doublets of the infrared bands for the pure D species sample at around 1066 cm(-1). This correlation band splitting width changed systematically depending on the D/H ratio and became a singlet for the sample with only 5 mol % D component. This systematic change in the splitting width of the infrared bands can be interpreted also reasonably based on the concept of the random existence of D and H chain steins in the crystal lattice. Although the details of the thermal behavior and the infrared band splitting are different between the alpha 1 and alpha 2 forms, the observed phenomena are essentially the same each other. Both of thermal and infrared data indicate reasonably the cocrystallization phenomenon of the D and H chain steins in the crystal lattice of the alpha 1 and alpha 2 forms when cooled from the melt, Suggesting a possibility of the random chain folding mode in the crystalline lamellae.