A novel X-type polyester containing 4-(2,2-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. The polyester is soluble in common organic solvents such as N,N-dimethylformamide and acetone. It shows a thermal stability up to 300 degrees C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 105 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of a poled polymer film at the 1064nm fundamental wavelength is 5.31 x 10(-9) esu. The dipole alignment exhibits a thermal stability even at 5 degrees C higher than glass-transition temperature (T-g), and no significant SHG decay is observed below 110 degrees C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.