A novel Y-type polyurethane 3 containing 4-(4-nitrophenylazo)catecholic groups as nonlinear optical (NLO) chromophores was prepared and characterized. Polyurethane 3 is soluble in common organic solvents such as acetone and DMF. Polymer 3 shows a thermal stability up to 270 degrees C from TGA thermogram and the T-g value obtained from DSC thermogram is around 96 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polymer film at 1064 nm fundamental wavelength is 4.58 x 10(-9) esu. The dipole alignment exhibits a thermal stability even at 4 degrees C higher than T-g, and there is no SHG decay below 100 degrees C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.