A solid electrolyte composition containing a sulfide-based solid electrolyte having conductivity of ions of metals belonging to Group I or II of the periodic table, a binder, and a dispersion medium, in which an amount of dissolved oxygen in the solid electrolyte composition is 20 ppm or less, a manufacturing method thereof, a storage method thereof, and a kit thereof, a solid electrolyte-containing sheet having a layer made of the solid electrolyte composition, a storage method thereof, and a kit thereof, and an all-solid state secondary battery.