Measurements on the third order optical nonlinearities of the conjugated polymeric cast film of PPQ (polyphenylquinoxalines) were performed based on the so called Z-scan method using a frequency doubled mode-locked Nd:YAG laser with low repetition rate.The nonlinear absorptive coefficient β=0.59 cm/MW,was obtained for PPQ,in addition,the measured nonlinear refractive index coefficient γ=2.4×10-12 cm2/W was in a good agreement with the previously reported value.