The synthesis of poly(2-methoxy-5-n-butoxy-p-phenylene vinylene) (MBPPV) via a dehydrochlorination of 2-methoxy-5-n-butoxy-alpha,alpha'-dichloro-p-xylene is described. The soluble polymer was characterized by elemental analysis, Fourier transform infrared (FTIR), H-1 nuclear magnetic resonance (NMR), and UV-visible spectroscopy. The energy gap (Eg) of the polymer was 2.53 eV determined by cyclic voltammogram. Light-emitting diode (LED) and light-emitting electrochemical cell (LEC) with the polymer were fabricated. The LED displayed unipolar I-V dependence with the turn-on voltage at 4.2 V. I-V curve of the LEC with poly(ethylene oxide) (PEO, Mw 2 x 10(4)) displayed mirror symmetry with the turn-on voltage at 2.7 V, but to the device with PEO (Mw 5 x 10(6)) no mirror symmetry was observed, the turn-on voltages at +2.7 V, -11.5 V. The emission maximum of the polymer in chloroform was at lambda = 550 nm, whereas the emission maxima of the LED at 5.2 V and the LEC at 4.8 V were at lambda = 566, 569 nm, respectively.