In this work, Sr2+ and Y3+ co-doped BaCeO3-based perovskite Ba0.9Sr0.1Ce0.85Y0.15O3-delta (BSCY) was synthesized by solid-state reaction method, and its mass transport behavior was studied using electrical conductivity relaxation (ECR) measurements in 600-800 degrees C range with respect to variations in oxygen partial pressure (pO(2)) and water vapor pressure (pH(2)O). During oxidation/reduction process, the electrical conductivity showed a monotonic relaxation behavior and in -2.65 <= log(pO(2)/atm) <= -0.67 range the values of oxygen chemical diffusivity ((D) over tilde (vO)) and surface exchange coefficient (kappa(vO)) varied in 10(-6)-10(-4) cm(2).s(-1) and 10(-4)-10(-2) cm.s(-1) range, respectively. However, during hydration/dehydration process, the electrical conductivity showed a non monotonic twofold relaxation behavior, and hydrogen, and oxygen chemical diffusivities ((D) over tilde (iH)) and ((D) over tilde (vH)) values were in 10(-5)-10(-3) and 10(-6)-10(-4) cm(2).s(-1) range, respectively, whereas hydrogen and oxygen surface exchange coefficient (kappa(iH)) and (kappa(vH)) values were in 10(-3)-10(-2) and similar to 10(-4)-10(-2) cm.s(-1) range, respectively. The comparison of H and O diffusivities of BSCY with BaCe0.83Y0.15O3-delta (BCY) showed that during hydration/dehydration the diffusivities of BSCY were lower than that of BCY. The long-term electrical conductivity measurement for similar to 800 h in humidified conditions showed a gradual decrease, which might be due to the gradual appearance of rhombohedral phase in otherwise orthorhombic BSCY, as confirmed by the X-ray diffraction (XRD) measurements. (C) 2016 Elsevier B.V. All rights reserved.