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 $240^{circ}C$ in thermogravimetric analysis with glass-transition temperature ($T_g$) obtained from differential scanning calorimetry near $116^{circ}C$. The second harmonic generation (SHG) coefficient ($d_{33}$) of poled polymer film at the 1064 nm fundamental wavelength is around $4.63{ imes}10^{-9}$ esu. The dipole alignment exhibits a thermal stability even at $4^{circ}C$ higher than $T_g$, and there is no SHG decay below $120^{circ}C$ due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.