In this paper is presented the study of electrodeposited polyterthiophenes with regular regiochemistry of substitution. The starting monomers were 3',4' and 3,3"-didodecyl 2,2':5',2" terthiophene. The presence of long alkylic chains improved the easiness of processability on the resulting polymers. Moreover, the symmetric structure of the monomers allowed a regular regiochemistry of substitution in the resulting polymers. Poly-didodecyl terthiophenes were electrochemically prepared from a mixture of acetonitrile and benzonitrile and then characterized with infrared spectroscopy, mass spectrometry, profilometry and scanning electron microscopy. Formal oxidation potential E-o and dimerization rate constants were determined for both monomers by means of ultrafast cyclic voltammetry (scan rate >5000 V s(-1)). The comparison of the results revealed the influence of substitution patterns in the determination of the polymerization degree and the kinetic of polymer growth during the electrochemical polymerization. The role of the monomers reactivities was then pointed out in the electrochemical synthesis,