Thermally stable nonlinear optical (NLO) polyimide prepolymers with different chromophore-loading levels were prepared through an addition reaction of bismaleimide 1 and N,N-diallylamino-substituted chromophore 2. The prepolymers were used to prepare NLO polyimide in a simultaneously poling/curing process. These prepolymers exhibited excellent film-forming quality and good solubility in low boiling-point solvents. Kinetic parameters (n, ln A, Ea) of their solidification reaction were determined by the dynamic method. Thermal and NLO properties of the cured polyimides with various chromophore-loading levels were studied. With increase of the chromophore-loading level, the glass transition temperature (T-g) and the thermal stability of the polyimides decreased, but the second-order nonlinearity of the poled film increased. The largest d(33) coefficient obtained was 76.2 pm/V at 1064 nm. The SHG signal was rather stable up to 120 degrees C.