A new X-type polyester 5 containing 4-(2-carbomethoxy-2-cyano)vinyl-5-nitrocatecholic groups as nonlinear optical (NLO) chromophores, which are parts of the polymer backbone, was prepared and studied its properties. Polyester 5 is soluble in common organic solvents such as acetone and dimethylsulfoxide. Polymer 5 shows a thermal stability up to 280 degrees C from thermogravimetric analysis with glass-transition temperature (T-g) obtained from differential scanning calorimetry of near 110 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polymer 5 film at the 1064nm fundamental wavelength is 6.13 x 10(-9) esu. The dipole alignment of polymer 5 exhibits a thermal stability up to 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.