Incorporation of Tb ions into the BaTiO 3 lattice was studied on ceramic samples with 5% Tb and Ba/Ti ratios of 0.987–1.053, using electron paramagnetic resonance (EPR) in combination with X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), and dielectric measurements. The EPR results provided direct evidence of the existence of Tb ions at Ti sites as Tb 4+ , which was characterized by a broad signal with g=~6.5 and an increased concentration of Ti-site Tb 4+ ions and a corresponding increase in the Ba/Ti ratio. The Raman charge effect at 805–833cm −1 and an EPR signal at g=2.004 associated with ionized Ti-vacancy defects provided the evidence for the existence of Tb ions at Ba sites as Tb 3+ . Because of the change in the Ba/Ti ratio, Tb ions in BaTiO 3 exhibited a self-adjustable amphoteric behavior with the mixed valence states of Ba-site Tb 3+ and Ti-site Tb 4+ utilized to preserve lattice electroneutrality. The ceramic density, morphology of grains, dielectric properties, and Raman charge effect were sensitive to the Ba/Ti ratio. The sample with a Ba/Ti ratio of 0.987 has evident advantages: a higher density, smooth-surfaced grains, lower dielectric loss, and low-temperature dielectric stability approaching to an X5R specification. Defect chemistry of Tb-doped BaTiO 3 is discussed.