2,5- Di-( 2'- hydroxyethoxy) benzylidenemalononitrile ( 3) was prepared and polyadded with 3,3'- dimethoxy- 4,4'- biphenylenediisocyanate to yield novel T- type polyurethane 4 containing 2,5- dioxy benzylidenemalononitrile group as a nonlinear optical ( NLO)- chromophore, which constituted parts of the polymer backbones. Polyurethane 4 was soluble in common organic solvents such as acetone and N, N- dimethylformamide. It showed a thermal stability up to 280 degrees C in thermogravimetric analysis thermogram and the glass- transition temperature ( T-g) obtained from differential scanning calorimetry thermogram was around 146 degrees C. The second harmonic generation ( SHG) coefficient ( d(33)) of poled polymer film at 1064cm (-1) fundamental wavelength was around 5.59 x 10(- 9) esu. The dipole alignment exhibited high thermal stability up to Tg, and there was no SHG decay below 140 degrees C because of the partial main- chain character of the polymer structure, which was acceptable for nonlinear optical device applications.