The rod-coil polymer of ethyl 4-[4’-oxy-4-biphenylylcarbonyloxy]-4’-biphenylcarboxylate with poly(ethylene oxide) with a degree of polymerization of 12 (12-4) was observed to exhibit a microphase-separated lamellar structure with nanoscale dimension and to melt into a layered smectic A mesophase. The complexes of 12-4 with 0.05-0.8 mol of LiCF3SO3 per ethylene oxide unit of a molecule were also prepared in order to investigate mesomorphic phase changes of 12-4 upon complexation. An abrupt mesophase change was observed for the entire range of salt concentrations. The complexes with 0.05-0.2 mol of LiCF3SO3 display an enantiotropic smectic A phase as their highest temperature mesophase. From the complex with 0.2 mol of LiCF3SO3, an enantiotropic cubic phase is induced and a smectic A phase disappears at the complex with 0.25 mol of LiCF3SO3, which displays a cubic mesophase only. The complex with 0.3 mol of LiCF3SO3 also exhibits an enantiotropic cubic phase; however, it exhibits a cylindrical micellar mesophase as its highest temperature mesophase, contrary to the complexes with up to 0.25 mol of LiCF3SO3. The complexes with 0.4-0.7 mol of LiCF3SO3 exhibit only a cylindrical micellar mesophase, and the complex with higher salt concentration becomes amorphous. These results, characterized by a combination of differential scanning calorimetry, optical polarized microscopy, and X-ray scattering experiments, are discussed.