Compositions based on CaCu 3+x Ti 4+y O 12 (x=+0.06, 0, −0.06; y=+0.08, 0, −0.08) with varying cation stoichiometry were prepared via the conventional solid state synthesis methods. No significant changes in the perovskite crystal structure were observed via diffraction compared to stoichiometric CaCu 3 Ti 4 O 12 (CCTO). However, a CuO phase was detected on the surface of all compositions and the presence of Cu 2 O was observed in the inner region of the sample for both Cu- and Ti-excessive CCTO. From the results of dielectric measurements, Cu- and Ti-deficient CCTO showed a higher dielectric constant than undoped CCTO. Due to the presence of Cu 2 O, both Cu- and Ti-excessive CCTO yielded low values of the dielectric constant. Using impedance spectroscopy, the improvement in dielectric constants and low tanδ values in the Cu- and Ti-deficient CCTO compositions can be traced to the lower grain resistivities compared to stoichiometric CCTO.