Novel Langmuir-Blodgett (LB) films were fabricated from mixed monolayers containing stearic acid and various poly(3-alkylthiophene)s, which contained almost 100% head-to-tail couplings. The LB films exhibited well-defined layered structures and self-organized properties of the regioregular polymers. The molecular organization, the layered structures and the electrical properties depended on the regioregularity and the length of the alkyl side chains of the regioregular polymers. The regioregular polymers have considerably improved the electrical conductivity and the third-order optical non-linearity.