The synthesis of a syndioregic main-chain hydrazone nonlinear optical polymer is reported. The nonlinearity is thermally stable up to 140 degreesC and retains 90% of the original value even when stored at 100 degreesC for 100 h. The polymer has a relatively low nonlinearity (d(33) = 3.6 pm/V) due to the incorporation of a low beta chromophore.