Soluble poly[(m-phenylenevinylene)-alt-(1,4-dibutoxy-2,5-phenylenevinylene)]s were synthesized via Wittig and Wittig-Horner reactions. The contents of trans-CH=CH linkages in the polymers were estimated to be either similar to 35% or similar to 88%, depending on the polymerization method used. Due to the large difference in the cis-/trans-olefin ratio, polymers 3 (cis-enriched) and 8 (trans-enriched) exhibited noticeable difference in their UV-vis spectra (Delta lambda (max) approximate to 19 nm) in THF solution. Their emission spectra, however, were essentially the same with the fluorescence lambda (em) at similar to 445 nm and a shoulder at similar to 471 nm. The shoulder in the emission spectra was resolved into a pronounced peak at low temperature. The low temperature emission spectra were also slightly red-shifted (similar to7 nm) in comparison with their room-temperature spectra. Despite their comparable solution phi (fl) values, a film of 3 emitted much stronger fluorescence than did its isomer 8.