Dielectric properties of undoped and manganese (Mn)-doped titanium dioxide (TiO2) ceramics were measured by various test methods including impedance spectroscopy techniques. It was found that direct current conductivity and dielectric loss were effectively suppressed by small amount (similar to 0.05 mol%) of Mn doping due to generation of possible electron traps. Further increase of Mn content led to formation of oxygen vacancies and increase of dielectric loss. Increased grain-boundary resistivity was observed as Mn-doping concentration increases, presumably due to segregation of Mn solutes at the grain boundaries. Larger difference between the grain and grain-boundary conductivity gave rise to space charge polarization. It was shown that TiO2 ceramics with optimum amount of Mn-doping concentration possess good dielectric properties that are suitable for energy storage applications.