Polymers with diverse chemical structure were evaluated to establish an empirical relationship between their thermo-optic coefficients (dn/d7) and coefficients of thermal expansion (a) according to the Lorentz-Lorenz equation. The results have showed that, regardless their chemical structure and T(g)s, all the evaluated polymers follow a single linear relationship between their dn/dT values and a values with the slope (delta n/delta T)(rho) equal to 0.56 and the interception (rho delta n/delta p)(T) equal to -3.7X10(-6). The relationship can be used to estimate the dn/dT value of a given polymer using its a value, which is widely available and can be easily measured using TMA and other conventional equipment, and the estimated dn/dT value is useful for developing polymers and evaluating device performance in optical waveguide applications. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved.