Amount of lead release from porcelain tableware, changes of the lead concentration distribution and the structure in the surface layer of the porcelain tableware during overglaze decoration firing in a water vapor atmosphere were investigated. Lead in the surface layer of the porcelain tableware was released by evaporation and surface exchange reaction between lead ions at the surface of the porcelain tableware and proton or hydronium ions in water vapor during firing in a water vapor atmosphere. Then the proton or hydronium ions introduced by the surface exchange reaction were released as water vapor formed by condensation reaction, and the silica-rich layer which contains α-quartz was formed at the surface This silica-rich layer was found to act as a protection layer against lead release.