The complex dielectric permittivity has been measured in the 10(3)-10(6) Hz frequency range for selected random copolyesters of poly(ethylene terephthalate). The variation of the dielectric properties with temperature has been qualitatively related mainly to two processes. The alpha relaxation, which is associated with the glass transition, has been shown to be dependent on the molecular order of the systems. The beta relaxation process has been assigned to local motions of the ester groups attached to both sides of the aromatic rings. The beta process is also shown to exhibit a dependence on molecular order.