Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)-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 280°C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry near 120°C. The second harmonic generation (SHG) coefficient (d 33) of poled polymer film at 1064 nm fundamental wavelength is 6.12 × 10−9 esu. Polymer 5 exhibits a high thermal stability even at 5°C higher than T g, and no significant SHG decay is observed below 125°C, which is acceptable for nonlinear optical device applications.