The complex χ ( 3 ) of toluene solutions of polydiacetylene, polyDCHD-HS, was measured by using Z-scan at λ=1064 and 1500nm and with picosecond pulses in order to estimate the potentials of this polymer for application to all-optical switching devices. The values of the real part of molecular hyperpolarizability γ were -2.3x10 - 4 7 and -3x10 - 4 7 m 5 /V 2 at 1064 and 1500nm, respectively. The nonlinear absorption could be better modeled with a three-photon process at both the wavelengths instead of the expected two-photon mechanism.