Dielectric constant and loss were studied for the &agr;‐relaxation of isotactic polystyrene (IPS). The decay function for the relaxation was calculated directly from the dielectric loss. It was found that the dielectric relaxation becomes slower as the degree of crystallinity increases. It was also found that the relaxation undergoes a crossover from a stretched exponential decay to a power law decay in the long time region as the relaxation proceeds.