By means of homogeneous stepwise condensation method, both the Ni-polyyne copolymers with PPh3 and PBu3 ligands, and modified pi-conjugated nickel-containing copolymers have been synthesized and confirmed by infrared (IR) analysis. The Ni-polyyne copolymers obtained are yellow powder having a (M) over bar(w), of about 1 similar to 2 x 10(4) and a molecular weight distribution (MWD) of less than 3, and they are soluble in tetrahydrofuran (THF), CHCl3, and toluene. Their third-order nonlinear optical properties have been investigated by a degenerate four-wave mixing (DFWM) technique. The effect of the nature of the ligands attached to the nickel atoms, the structure, and the length of pi-conjugation between the 2 metal centers in the main chain on the hyperpolarizability gamma of the Ni-polyyne polymers have been discussed. The maximum susceptibility chi((3)) and hyperpolarizability gamma of the Ni-polyyne polymers reach 5.17 x 10(-12) and 2.30 x 10(-30) esu, respectively.