ABSTRACTA new Y-type polyurethane (4) containing nitrothiazolylazoresorcinoxy groups as NLO chromophores, which are components of the polymer backbone was prepared. Polyurethane 4 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 240°C from thermogravimetric analysis with glass-transition temperature (Tg) obtained from differential scanning calorimetry near 126°C. The second harmonic generation (SHG) coefficient (d33) of poled polymer films at the 1064 nm fundamental wavelength is around 9.02 × 10−9 esu. The dipole alignment exhibits a thermal stability even at 4°C higher than Tg, and no SHG decay was observed below 130°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.