CaCu3Ti4O12–polyethersulfone (CCTO–PES) composites with various CCTO volume fractions up to 0.5 were prepared. Relatively high dielectric constant (ε = 32.7) and low loss (tan δ = 0.063) of the composites with CCTO volume fraction at 0.5 were observed. Various theoretical models were employed to predict the dielectric constant of these composites, the dielectric constant obtained via EMT model were in close agreement with the experimental data. The dielectric constant of CCTO–PES composites showed weak frequency dependence at the measuring frequency range, and the loss tangent apparently decrease with increase in frequency. Both the dielectric constant and loss tangent showed weak temperature dependence at low temperature range from 20 to 60 °C, however, they increased dramatically with a further increase in temperature above 60 °C.