The dielectric dielectric relaxation of oxygen vacancies in the Ca doped BaTiO3 system has been studied. Curie point (T-c) of Ba(Ti1-xCax)O3-x shifted to lower temperatures as Ca content (x) was increased. At lower frequencies (<1 kHz), dielectric constants steeply decreased with increasing frequency. At >1 kHz, dielectric constants were independent of frequency regardless of Ca-doping levels. Dielectric loss (tan delta) peaks moved to higher frequencies with increasing Ca content (x) in the Ba(Ti1-xCax)O3-x system (0.0 <= x <= 0.02) at 300 degrees C. The activation energy was estimated to be 0.38-0.65 eV at 200-300 degrees C and 0.72-1.04 eV at 350-500 degrees C. The activation energy at higher temperatures could be due to the extra energy required for the extended motion of oxygen vacancies in addition to the swing motion around the defect center (Ca ''(Ti)). (C) 2010 Elsevier B.V. All rights reserved.