The giant dielectric and nonlinear current-voltage properties of CaCu 3 Ti 4 O 12 (CCTO) incorporating Portland cement (PC) were investigated. Analysis revealed that the microstructure of the CCTO/PC ceramics was highly dense. Using the microstructure analysis and theoretical calculation, the elements in PC (i.e., Al, Si, Fe, K, Cr, and Mg) can substitute into the CCTO structure, giving rise to enhanced electrical properties of the grains and grain boundaries. As a result, the giant dielectric and nonlinear current-voltage properties of CCTO/PC were significantly improved. The low-frequency loss tangent of CCTO/PC was greatly reduced, by a factor of 10, while the dielectric permittivity of the ceramics was still large (∼10 4 ) over a frequency range of 10 2 -10 6 Hz. Interestingly, the nonlinear coefficient (α) and electric field breakdown (E b ) of the CCTO/PC ceramics were greatly enhanced by factors of 2 and 30, respectively. Impedance spectroscopy analysis revealed large increases in α and E b , as well as a decrease in the loss tangent due to a significant increase in the grain boundary resistance of CCTO/PC ceramics. Changes in giant dielectric and nonlinear electrical properties can be well described by the internal barrier layer capacitor model based on space charge polarization at the internal interfaces.