A first rosin-based nonlinear optical polymer was synthesized by the condensation polymerization of rosin-maleic anhydride imidodicarboxylic acid (RMID) with (4'-nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]-aniline (DR 19). The polymer was amorphous and showed glass transition at 184℃. It was soluble in various organic solvents such as methylene chloride, chloroform, and tetrahydrofuran. Thin film of high optical quality could be prepared from these polymer solutions by spin-coating. Dipolar alignment of nonlinear optical chromophores was achieved by the contact poling at the glass transition temperature of the polymer Electro-optic coefficient (r₃₃) of this poled polymer film at a wavelength of 632.8 nm was measured to be 11 pm/V, which showed virtually no relaxation at 80℃ for more than 100 h after the initial 15% decay.