A novel Y-type polyester 4 containing 5-methyl-4-{5-(1,2,2-tricyanovinyl)-2-thiazolylazo}resorcinoxy groups as nonlinear optical (NLO) chromophores was prepared and characterized. Polyester 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows a thermal stability up to 250 degrees C from thermogravimetric analysis thermogram with a glass-transition temperature (Tg) obtained from differential scanning calorimetry thermogram of around 94 degrees C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at 1064nm fundamental wavelength is 8.12x10-9esu. The dipole alignment exhibits a thermal stability even at 6 degrees C higher than Tg and there is no significant SHG decay below 100 degrees C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.