Thermal relaxation properties of a poled polyester containing carbazole nonlinear optical chromophores in the main chain have been studied. The polymer has two acceptor groups in the 3- and 6- positions of carbazole ring, and the net dipole moment is perpendicular to the polymer backbone. The decays of second-harmonic intensities at different temperatures were monitored after the removal of electric field. The decay of second harmonic intensity consists of fast and slow processes. These two processes can be attributed to the small-scale local orientation of individual chromophores around the polymer backbone, and the large-scale gross orientation due to micro-Brownian motion of the main chains, respectively. The decay characteristics were well fitted to a relaxation function which consists of a stretched exponential and a single exponential functions.