An all-solid secondary battery, comprising: a cell comprising a positive electrode active material layer, a negative electrode active material comprising at least one of lithium metal and a lithium-containing alloy, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein a ratio of volume density to true density of the positive electrode active material layer is about 0.6 or greater, wherein a ratio of volume density to true density of the solid electrolyte layer is about 0.6 or greater, and wherein an average pressure applied to opposite sides of the solid electrolyte layer in a fully discharged state is greater than 0 megapascals and 7.5 megapascals or less.