A series of poly (heteroarylene methines) containing one pyrrole or thiophene ring alternating with a carbon atom in the main chain were synthesized. The resonant third-order optical nonlinearity at 532nm was studied by using degenerate four-wave mixing (DFWM) techique. The resonant secondorder hyperpolarizabilitiesγ and third2order nonlinear optical susceptibility χ(3) were up to 10-30esu and 1028esu respectively. Poly {pyrrole2[ 2,52diyl (p2N,N2dimethlamino) benzylidene]} (PPDMAB) was chosen to be further studied mainly due to its good solubility and filmforming performance. Time2resolved Optical Kerr effect (OKE) of PPDMAB was investigated with femtosecond laser pulses at 790 nm. Only an ultrafast component of OKE of PPDMAB was observed and its dephasing time was 84.7 fs, which is attributed toπelectron-cloud distortion occurring upon the non-resonant excitation. The off-resonant second-order hyperpolarizabilitiesγ and third-order nonlinear optical susceptibility χ(3) of PPDMAB were also determined by transient OKE. The results show that PPDMAB exhibit large off2resonant nonlinearities γ as large as γ=5.78×10-32esu, for each structural units and χ(3) as large as χ(3)=1.26×10-10esu for the material have been obtained.