Maskless fabrication of periodic patterns of a conjugated polymer is achieved by regioselective condensation of 2,5-diiodothiophene on chemically patterned substrate surfaces followed by in situ photochemical conversion of the condensed molecules into oligothiophenes and polythiophenes. This approach utilizes preferential aggregation of monomer molecules on the substrate that is periodically patterned with wetting regions surrounded by nonwetting regions. Since the monomer molecules are confined in the specific regions on the substrate, the polymer patterns can be produced at those locations by blanket irradiation of UV light without mask. The effects of wettability contrast and the dimension of periodicity are important factors for good pattern recognition during the monomer deposition.