A regio-controlled poly(2,5-dimethyl-1,4-phenylene ether) was successfully prepared by the oxidative coupling polymerization of 2,5-dimethylphenol using di-mu-hydroxobis[(N,N,N',N'-tetramethylethylenediamine) copper(II)] as a catalyst under oxygen. The catalyst effectively promoted the regio-controlled polymerization even at the concentration of 0.1 mol % to the monomer, and the resulting polymer showed a melting temperature at 280 degrees C.