||Nonlinear optical (NLO) polymers are considered as a promising candidate for making electro-optic (EO) devices, mainly because they offer many advantages such as light weight and good processability to form EO devices. Main-chain polymers have good thermal stability of dipole alignments, but they often do not dissolve in organic solvents, which make them impossible to fabricate stable noncentrosymmetric films. Side-chain NLO polymer systems have the advantages such as good solubility and high level of NLO chromophore relative to the main-chain systems, but they often suffer from poor stability of dipole alignments at high temperatures. In this work we prepared novel Y-type polyester containing 2,4-dioxybenzylidenecyanoacetate as a NLO-chromophore, which constitutes a part of polymer backbon. The resulting polymer was soluble in common organic solvents. NLO activity of poled polymer films and their thermal stability will be presented in the report.