Trivalent-cation-doped BaCeO3 has fairly high protonic conductivity at intermediate temperatures. This paper deals with the effects of the kind of dopant, M in BaCe0.9M0.1O3-alpha (M = Y, Tm, Yb, Lu, In, or Sc), on the electrical (ionic) conductivity at 400 - 900 degrees C and chemical stability. It was found that the two properties are both governed by the ionic radii of the dopants and are in a trade-off relation. The electrical conductivity seems to be also affected by the electronegativity of the dopant element, i.e., the conductivity increases with increasing ionic radius and decreasing electronegativity (increasing basicity). (c) 2007 The Electrochemical Society.