The temperature and frequency dependence of dielectric properties of A-site lower valence cation Na-doped Barium strontium titanate (Ba1-xNax)(0.9)Sr0.1TiO3-delta (x = 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 and 03) ceramics have been investigated up to 450 degrees C from 100 Hz to I MHz. Other than dielectric properties at low temperature, the relaxation behavior above 150 degrees C for all the compositions was observed with broad dielectric peaks epsilon' (T), tan delta(T) and epsilon' (f). The universal dielectric response associated with the activation energy of 0.79-0.98 eV and complex impedance properties indicate that with the increasing of Na, the concentration of oxygen vacancies inhabiting grain boundary increases and under thermal stimulation the tunneling effect of oxygen vacancies strengthens, which dominate for the relaxation at high temperatures. (C) 2014 Elsevier B.V. All rights reserved.