Stability of the electro‐optic coefficient of a poled and cross‐linked nonlinear optical polymer is reported at 85, 100, and 110 °C. The observed decay, which is due to orientational relaxation of the nonlinear optical dyes in the films, is discussed in terms of several proposed models. The introduction of a continuously varying relaxation time, which occurs when considering physical agingduringthe stability tests, is observed to account for orientational relaxation over a long time period. ©1995 American Institute of Physics.