The syntheses of bis(trihalophenolato)di(pyridine) nickel(II) complexes were achieved in aqueous solution, and their characterizations were performed by Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible analysis, differential scanning calorimetry, and elemental analysis. The thermal polymerization of these complexes was studied in toluene solution in the presence of iodine. The effect of time, temperature, and amount of iodine added on the percentage conversion, structure of polymers, and intrinsic viscosity ([eta]) were investigated. Polymers were characterized by FTIR, H-1-NMR, and C-13-NMR spectroscopic analyses, glass-transition temperatures determined by differential thermal analysis, and [eta] values determined by the viscometric method.