The third order optical nonlinearity, x(3), of two polymers consisting of nickel dithiolene guest molecules in a polymethylmethacrylate host have been measured. The optical nonlinearity was measured by degenerate four wave mixing experiments at a wavelength of 1.06 μm using 100 ps laser pulses. χ(3)coefficients of up to 10−17m2/V2were observed corresponding to nonlinear refractive index, n2, of up to 10−8cm2/KW with a damaged threshold > 1GW/cm2.