Differential scanning calorimetry (d.s.c.) measurements on the 50/50 blends of well-defined multibranched polystyrenes and linear polystyrenes were carried out to investigate the miscibility between polymer components having the same constitutional repeating units but different molecular architectures. Multibranched polystyrenes with different branch number and length were prepared by the radical polymerization of polystyrene macromonomers of different molecular weights possessing a different polymerizable end group, i.e. a vinylbenzyl end group and methacryloyl end group. D.s.c. curves showed one or two thermal transitions corresponding to the glass transitions depending on both the branching architecture of the multibranched polystyrene, namely poly(macromonomer)s, and the molecular weight of the linear polystyrenes. The miscibility between the poly(macromonomer) and the linear polystyrenes decreased with increase in both branch number of poly(macromonomer)s and the molecular weight of the linear polystyrene. The miscibility increases with increase in the branch length but was not much influenced by the chemical structure of the central backbone of the poly(macromonomer)s. These results indicate that the miscibility in the athermal binary multibranched-linear polystyrene blends is influenced by the branching architecture, and the blends locate near the miscible/immiscible boundary.