2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine to yield novel Y-type polyimide 5 containing 2,3-dioxybenzylidenemalononitrile group as NLO-chromophores, which constitute parts of the polymer backbones. The resulting polyimide 5 was soluble in polar solvents such as acetone and N,N-dimethylformamide. Polymer 5 showed a thermal stability up to 330 degrees C in thermogravimetric analysis thermogram with T (g) value obtained from differential scanning calorimetry thermogram near 190 degrees C. The second harmonic generation (SHG) coefficient (d (33)) of poled polymer films at the 1064 nm fundamental wavelength was around 3.15x10(-9) esu. The dipole alignment exhibited a thermal stability even at 20 degrees C higher than the glass-transition temperature, and there was no SHG decay below 210 degrees C because of the partial main chain character of polymer structure, which was acceptable for nonlinear optical device applications.