Novel X-type polyester containing 4-(2,2-dicyanovinyl)-6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyester is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester shows a thermal stability up to 300 degrees C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 108 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polyester film at the 1064nm fundamental wavelength is 7.13 x 10(-9) esu. The dipole alignment exhibits a thermal stability even at 7 degrees C higher than glass-transition temperature (T-g), and no significant SHG decay is observed below 115 degrees C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.