Alternating copolymers, poly(p-phenylene[3-(alkylthio)-2,5-thienylene]-p-phenylene)s (4) were prepared by the nickel-catalyzed polymerization of 3(alkylthio)-2,5-bis(4-chlorophenyl)thiophenes (3). Polymerizations were conducted in N-methyl-2-pyrrolidinone (NMP) in the presence of nickel chloride, zinc, triphenylphosphine, and 2,2’-bipyridine under mild conditions. The resulting polymers 4 had a weight-average molecular weight up to 47 000. The microstructure of polymers was investigated by C-13-NMR spectroscopy, and it has been found that the obtained polymers had the expected regiorandom structures. The polymers were readily soluble in chloroform, dichloromethane, and THF and can be processed into uniform films from their solutions. Degenerate four-wave mixing measurements on polymer 4b yielded a third-order susceptibility as high as 5.5 x 10(-11) esu.