Abstract: Process for the preparation of a sodium paraperiodate wherein an iodine compound is converted into the sodium paraperiodate in the presence of Na.sup.+ ions by means of an alkali metal hydroxide and an alkali metal hypochlorite. The iodine compound is applied in the form of an iodine-containing mixture in which besides the iodine compound in the form of I.sub.2, iodide or iodate compounds, one or more compounds chosen from the group of chlorides, bromides, sulphates, sulphites, carbonates, bicarbonates, nitrates and dissolved organic components are also present. The invention also relates to the preparation of sodium metaperiodate and other alkali and alkali earth metal periodates, wherein the sodium paraperiodate obtained is converted into sodium periodate or into an alkali or alkali earth metal periodate by means of an acid or an alkali and alkali earth metal salt at an elevated temperature. The acid used preferably is HNO.sub.3.