Coil-rod-coil molecules were prepared to have identical coil volume fraction (f = 0.78) relative to mesogenic rod segment, but different coil segments, i.e., poly(propylene oxide) with DP = 13 and poly(ethylene oxide) with DP = 18. Their self-assembly behavior in the solid and liquid crystalline phases was investigated using optical polarized microscopy and small-angle X-ray scattering techniques. The coil-rod-coil molecule with the poly(propylene oxide) coils shows a 3-D body-centered tetragonal micellar structure in both solid and liquid crystalline phases. In contrast, the coil-rod-coil molecule with the poly(ethylene oxide) coils exhibits a 3-D honeycomb-like lamellar structure in both solid and liquid crystalline phases. These results demonstrate that the cross-sectional area of coil significantly influences the self-assembly behavior of rod segments even at constant coil volume fraction relative to rod segment and provides the way to fine-tune 3-D supramolecular structures in the rod-coil system.