The dielectric relaxation behavior of copolymers of styrene and butyl acrylate is investigated over a wide frequency range. The results are analyzed in terms of the free volume and configurational entropy theories. The calculated fractional free volume was nearly constant over the composition range studied while the volume expansion coefficient exhibits a maximum in the mid composition range. Even though the change in heat capacity at T-g varied linearly with composition, the free energy of activation calculated from the configurational entropy model reached a broad maximum in the mid composition range. In addition, the average dielectric relaxation time of the copolymers at T-g is not constant. In fact, the longest relaxation times were obtained for samples containing nearly equal amounts of styrene (S) and butyl acrylate (B). It is suggested that the SB diad has a relaxation time much longer than the relaxation times of the SS and BB diads.