A novel π-conjugated polypyrrole derivative-poly{(pyrrole-2,5-diyl)[p-nitrobenylidene]} (PPNB) is synthesized. Its solution in N-Methyl-2-pyrrolidone (NMP) and its thin film combined with polyvinyl alcohol (PVA) are respectively prepared. With 532 nm, 8 ns laser pulse as pumping beam and He-Ne laser beam (632.8 nm, CW) as probing light, the nonlinear optical response times of the PPNB solution and film are measured. The building-up times of the laser induced refractive index change of the PPNB/NMP solution and the PPNB/PVA film are measured to be 4 μs and 5 μs, respectively. Their recovering times are 30 ms and 5 ms, respectively. This optical nonlinear phenomenon may be mainly dominated by the thermo-optical nonlinear effect.