[en] New Y-type polyester (3) containing nitrophenylazoresorcinoxy groups as NLO chromophores, which are components of the polymer backbone, was prepared and characterized. Polyester 3 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. It shows a thermal stability up to 240 .deg. C in thermogravimetric analysis with glass-transition temperature (T_g) obtained from differential scanning calorimetry near 116 .deg. C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1064 nm fundamental wavelength is around 4.63 x 10^-9 esu. The dipole alignment exhibits a thermal stability even at 4 .deg. C higher than T_g, and there is no SHG decay below 120 .deg. C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications