Third-order optical nonlinearity of Ni-azo metal complex in solution was investigated by the Z-scan technique with 38 ps laser pulse excitation at 1.064 μm. Self-defocusing was observed, and third-order nonlinear susceptibility χ(3)pure and the second hyperpolarizability were measured to be 1.8×10-11 esu and 1.0×10-32 esu, respectively.