The length of the alkyl-groups affects both the spectrophotometric and the electrochemical properties of poly(alkoxy-alkyl-terthiophenes) films prepared by cyclic voltammetry. The maximum absorbance shifts towards higher wavelengths and the oxidation peak towards cathodic potentials as the alkyl-chain length increases. Moreover, it was found that the photoelectrical performance exhibited by poly(alkoxy-alkyl-terthiophenes)-based devices improved from poly(4,4''-dipenthoxy-3'-dodecyl-2,2':5',2''-terthiophene) to poly(4,4''-dipenthoxy-3'-hexyl-2,2':5',2''-terthiophene), probably due to an increasing hopping mobility, and remained constant or somewhat decreased by going from poly(4,4''-dipenthoxy-3'-hexyl-2,2':5',2''-terthiophene) to poly(4,4''-dimethoxy-3'-methyl-2,2':5',2''-terthiophene) possibly for a lower planarity of polythiophene chains.