The microstructural changes and dielectric properties of CaGaxCu3-xTi4O12(x= 0, 0.01, and 0.05) ceramics were investigated. The mean grain size and dielectric constant of CaGa0.01Cu2.99Ti4O12ceramic increased by roughly a factor of 40, but decreased by roughly a factor of 100 with increasing levels of Ga3+doping corresponding to the CaGa0.05Cu2.95Ti4O12ceramic. The resistance of grain boundaries of CaGa0.01Cu2.99Ti4O12ceramic decreased significantly. As levels of Ga3+doping increased (x = 0.05), the resistance of grain boundaries was enhanced greatly. The giant dielectric response in CaGaxCu3-xTi4O12ceramics can be well described based on their electrically heterogeneous microstructure and was found to be correlated with their microstructure. [ABSTRACT FROM AUTHOR]