The phase behavior of (A-B)/(A-C) binary blends capable of hydrogen bonding between B and C blocks was investigated, focusing on the degree of hydrogen bonding power. Two kinds of binary blends (PS-b-P4VP/PS-b-PHS and PS-b-P2VP/PS-b-PHS) were employed. It was observed by small-angle X-ray scattering (SAXS) and TEM that the PS-b-P4VP/PS-b-PHS blend formed asymmetric lamellar morphology at more asymmetric volume fraction where PS-b-P2VP/PS-b-PHS blend could not form. By comparing the experimentally observed morphology with theoretically predicted morphology by the SST model, we estimated of P4VP/PHS to be -0.17 and Flory-Huggins segmental interaction parameter of P2VP/PHS to have a value between -0.05 and -0.075. Flory-Huggins segmental interaction parameter P4VP/PHS was greater than that of P2VP/PHS. From the strong stretching Theory (SST) model, extremely large asymmetric lamellar morphology could be achieved when very large favorable intermolecular force between B and C blocks is introduced.