The novel Cl(- )doped compound based on oxygen deficient double perovskite Ba2CaNbO5.5 was synthesized Ba2CaNbO5.48Cl0.05 and its structure, thermal properties, hydration behavior and electrical properties have been investigated. It was found that introduction of Cl(- )ions leads to the increasing of oxygen ion and proton conductivities. The appearance of donor defect Cl-o(center dot)(or F-o(center dot)) decreases the activation energy for oxygen ion transport and increases the mobility of oxygen vacancies due to electrostatic repulsion between the positive charged defects V(o)(center dot center dot)and Cl-o(center dot)(F-o(center dot)). It was shown that Cl(- )doping decreases proton concentration but enhances proton conductivity due to significant increase in proton mobility.