An optically active levoazobenzene polyurethane (PU) was synthesized and was based on the chromophore 4-(4'-nitrophenylazo) phenylamine, the chiral reagent L(-)-tartaric acid, and toluene diisocyanate. The chemical structure and thermal properties were characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, H-1-NMR spectroscopy, and differential scanning calorimetry. The PU had high number- and weight-average molecular weights up to 52 300, a large glass-transition temperature of 235.7 degrees C, and an optical rotation of -18.06 degrees, The optical parameters, including the refractive index (n) and thermo-optic coefficient (dn/dT); the dielectric constant (epsilon) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn/dT and epsilon values for the polymer were in the range -4.1200 to 3.6257 x 10(-4) degrees C-1 and 2.00 +/- 0.11, respectively. The dn/dT values were one order of magnitude larger than those of inorganic glasses, such as zinc silicate glass (5.5 x 10(-6) degrees C-1) and borosilicate glass (4.1 x 10(-6) degrees C-1), and were larger than organic materials, such as polystyrene (-1.23 x 10(-4) degrees C-1) and poly(methyl methacrylate) (-1.20 x 10(-4) degrees C-1). The epsilon values were lower than that of alicyclic polyimide and semiaromatic polyimide. The obtained PU is expected to be useful for optical switching and optical waveguide areas. The conclusion has a little significance for the development of a new digital optical switch. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 146-151, 2010