Novel X-type polyurethane 5 containing 4-(2 '-carbomethoxy-2 '-cyano)vinyl-6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stabilities up to 260 degrees C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry near 108 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polymer film at 1064nm fundamental wavelength is 9.83 x 10(-9) esu. Polymer 5 exhibits a high thermal stability even at 2 degrees C higher than T-g, and no significant SHG decay is observed below 110 degrees C, which is acceptable for nonlinear optical device applications.