A new Br- anion-conducting solid electrolyte with a low solubility in water and a high thermal stability at elevated temperatures was developed by selecting lanthanum oxybromide (LaOBr) as a mother solid electrolyte phase. By the partial substitution of La3+ site in LaOBr with divalent Ca2+ or Sr2+, the bromide anion conductivity was greatly enhanced, and the highest Br- ion conductivity of 1.9 x 10(-3) and 1.2 x 10(-4) S . cm(-1) was obtained at 873 K for La0.9Sr0.1OBr0.9 and La0.9Ca0.1OBr0.9 respectively. The Br- anion conduction in La0.9M0.1OBr0.9 (M=Ca, Sr) was directly demonstrated by DC electrolysis. 0 2004 Elsevier B.V. All rights reserved.