(Nb+Al) co-doped SrTiO3 ceramics with a nominal composition of Sr(Nb0.5Al0.5)(x)Ti1-xO3 (x = 0, 0.02, 0.04, and 0.06) were fabricated using the conventional solid-state reaction method; giant permittivity (10500) and low dielectric loss (0.03) were obtained at x = 0.06. Dielectric and impedance spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, were employed to study why the dielectric property improved. The results indicate that the giant dielectric response occurs because of the combined effects of the off-center Ti3+ reorientation and conduction of electrons with the polar ordering structure Ti3+/Ti4+. In contrast, the low dielectric loss can be attributed to electron localization that occurs because of the defect dipole mml:mfenced close=] open=[ separators="Ti4+e-:msubsup Vol:msub -Ti4+efenced>. These fundamental understandings will benefit the design of doped SrTiO3 ceramics with desired performance.