In this work, we present a complete study of BaSn1−xYxO3−δ (x=0-0.50) compounds putting emphasis on transport properties as determined by impedance spectroscopy under controlled atmosphere. The measurements of transport properties reveal a p-type behavior in oxidative atmosphere and a pure ionic behavior in slightly reducing one. In strongly reducing conditions, the samples tend to be electron-conductive at high temperature. In wet atmosphere, the thermogravimetry and electrical measurements confirm the incorporation of protons and their predominance as charge carrier at low temperature. The higher bulk proton conductivities are observed for the higher yttrium contents, which is due to the increased amount of charge carriers. After applying different thermal treatments, we confirm that these samples tend to decompose in wet conditions and that low yttrium contents are desirable to increase the stability. The good stability in CO2-containing atmosphere is also confirmed. This work illustrates that an optimal value for yttrium content exists that allows obtaining a significant proton conductivity and sufficient stability. ©