New Y-type polyimide (4) containing nitrophenylazoresorcinoxy groups as NLO chromophores, which are components of the polymer backbone, was prepared and characterized. Polyimide 4 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 290 degrees C in thermogravimetric analysis with glass-transition temperature (T-g) obtained from differential scanning calorimetry near 128 degrees C. The second harmonic generation (SHG) coefficient (d(33)) of poled polymer film at the 1064 nm fundamental wavelength is around 5.46 x 10(-9) esu. The dipole alignment exhibits a thermal stability up to T-g, and there is no SHG decay below 130 degrees C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.