An electrolyte sheet for solid oxide fuel batteries which has mechanical strength characteristics including a high and stable average value of strength and a high and stable Weibull coefficient and which has high adhesion to an electrode formed on a surface thereof and hence inhibits the electrode from suffering interfacial separation from the electrolyte sheet. The electrolyte sheet for solid oxide fuel batteries is characterized by having a plurality of recesses and/or protrusions on at least one surface thereof, the recesses and protrusions having base faces which are circular or elliptic or are a rounded polygon in which the vertexes have a curved shape with a curvature radius of 0.1 [mu]m or larger and/or the recesses and protrusions having a three-dimensional shape which is semispherical or semiellipsoidal or is a polyhedron in which the vertexes and the edges have a curved cross-sectional shape having a curvature radius of 0.1 [mu]m or larger. The electrolyte sheet is further characterized in that the base faces of the recesses and protrusions have an average equivalent-circle diameter of 0.5-250 [mu]m, that the average depth of the recesses and the average height of the protrusions are 0.3-50 [mu]m each, and that the average thickness of the sheet is 100-400 [mu]m.