Self-assembled structures in solvent-cast mixtures of polystyrene-block-poly(ethylenepropylene) (PS-PEP) and polystyrene-block-(partially hydrogenated polyisoprene) (PS-HPI) were investigated by small-angle X-ray scattering and transmission electron microscopy. Various self-assembled structures were observed in the solution-cast films, depending upon the degree of hydrogenation of the HPI block of the PS-HPI. The microdomain structure of PS domains and domains composed of PEP and HPI (called "rubber domains" hereafter) was first formed at relatively low polymer concentrations during the solvent-casting process over the whole range of the hydrogenation in our experiments. Subsequently, at a higher concentration during the process, phase separation between PEP and HPI in the rubber domains was observed in mixtures with medium and high hydrogenation. For mixtures with low hydrogenation, repulsive interactions between PEP and HPI become large enough to cause the segregation between PEP and HPI, which leads first to the modulation of the interface between the PS domain and the rubber domain and eventually to the macrophase separation between PS-PEP and PS-HPI, during the solvent evaporation process. Thus, observed macrophase-separated structure is a consequence of a two-step phase separation, i.e., a microphase separation followed by a macrophase separation. The development of those patterns was controlled only by the degree of the repulsive segmental interaction between PEP and HPI, i.e., the degree of the hydrogenation of HPI.