Dielectric constant and ac conductivity of Polyester doped with carbon black are investigated in the frequency range (0.5-103) KHz and within the temperature range (26-80) oC. Dielectric permittivity and loss tangent reduced with increasing frequency and increase with increasing temperature. The ac conductivity σac for all samples were found to be weak frequency dependent at low frequency, however vary with frequency as a power law ωs at higher frequency range. The variation of frequency exponential factor s between 0.63 and 0.77, indicates a dominant hopping process at low temperatures. From the temperature dependence of dc conductivity, the increase of activation energy was observed with carbon black concentrations.