A new Y-type polyester (3) containing nitrophenylazoresorcinoxy groups as NLO chromophores, which are components of the polymer backbone was prepared. Polyester 3 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. It shows a thermal stability up to 240 degrees C from thermogravimetric analysis with glass-transition temperature (Tg) obtained from differential scanning calorimetry near 116 degrees C. The second harmonic generation (SHG) coefficient (d33) of poled polymer films at the 1064nm fundamental wavelength is around 4.63x10-9esu. The dipole alignment exhibits a thermal stability even at 4 degrees C higher than Tg, and no SHG decay was observed below 120 degrees C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.