The present invention relates to a process for preparing poly (3,4-alkylenedioxythiophene) derivatives of the formula I:wherein X represents –CH2CH2R'- or CH2C(RR’)CH2-, wherein R represents hydrogen or -CH2-(CH2)A-B or -CH2-X-(CH2)A-B, wherein A represents 0 to 10 and B represents a hydrogen or a C1-C5 linear or branched alkyl group or a C1-C5 aryl group optionally substituted by one or more groups selected from amines, carboxylic acids, alcohols, propargyl, azide, ethers, sulfonic acids, thiols or amides; R’ represents R as defined above or C1-C3 linear or branched alkyl group or aryl group optionally substituted by one or more groups selected from aryl, propargyl or azide n is the number of recurring or repeating units in the polymer. The process is carried out in the presence of a Palladium-ligand complex catalyst of the formula Pd(0)-L4, wherein L represents a ligand.