Poly(p-phenylene vinylene) derivatives substituted with a long side chain containing alkoxybiphenyl mesogenic unit have been synthesized and its electrical and optical properties have been studied. A liquid-crystalline molecular alignment and layer structure have been confirmed by optical microscopic observation and X-ray diffraction measurement, respectively. The dielectric constant changes in a stepwise manner at phase transition temperature. The bandgap of this new polymer in the liquid-crystalline phase has been evaluated to be about 2.3 eV, which monotonously decreases with decreasing temperature. It has been found that the emission spectra of electroluminescent diode using this new liquid-crystalline polymer as an emissive layer depend on the polarity of the applied voltage.