A simple and generally applicable new synthetic method to prepare second-order nonlinear optical (NLO) polyimides has been developed. In this approach, sidechain-substituted polyimides were synthesized via isocyanato-terminated prepolymers prepared directly from NLO chromophore-containing diols Disperse Red 19. Using this technique, the tedious synthesis of the classical diamine monomers and harsh imidization process associated with polyamic acid prepolymers are avoided. The resulting polymers possessed good solubility and high glass-transition (171-211 degreesC) and thermal-decomposition temperatures. The polymers also exhibited excellent film-forming properties, and good optical-quality films were easily obtained by spin coating. The second-order NLO activities of the polymer films were also studied, and several factors that might determine the growth of the second-order NLO activity were proposed. The polymers obtained exhibit a large second-order NLO activity (34-52.5 pm/V at 1064 nm).