Nonlinear currentvoltage properties of CaCu3Ti4O12 ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu3Ti4O12 resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu3Ti4O12 ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of similar to 29.67 and breakdown electric field strength of similar to 1.52x10(4) V/cm were obtained in the Ca0.775Tb0.15Cu3Ti4O12 ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.