2,5-Di-(2'-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride to yield novel T-type polyester (4) containing 2,5-dioxybenzylidenemalononitrile groups as NLO-chromophores, which are parts of the polymer backbones. The resulting polymer 4 was soluble in common organic solvents such as acetone and DMF and showed thermal stability up to 280 A degrees C with T (g) of 83 A degrees C. The second harmonic generation (SHG) coefficient (d (33)) of poled polymer film at the 1,064 nm fundamental wavelength was around 4.46 x 10(-9) esu. The dipole alignment exhibited high thermal stability even at 10 A degrees C higher than T (g), and there was no SHG decay below 95 A degrees C due to the partial main-chain character of polymer structure, which was acceptable for NLO device applications.