A new three-dimensional hyperbranched polymer with 4-(2-cyano-2-methoxy-carbonylvinyl)aniline as a second-order nonlinear optical chromophore has been synthesized starting from 4-formyl-N,N-di(2-hydroxyethyl)aniline and cyanoacetic acid by a one-pot Knoevenagel polycondensation using 4-(dimethylamino)pyridine as a base. This hyperbranched polymer with a good solubility in polar organic solvents, such as N,N-dimethylformamide and methyl sulfoxide, was characterized by H-1 n.m.r., i.r. and u.v.-vis spectroscopies. Differential scanning calorimeter analysis showed that this polymer exhibited a glass transition temperature at 86 degrees C. The second-harmonic generation signal has been observed from the poled films of this hyperbranched polymer.