The present invention provides: a freeze-dried composition which comprises (a) a monovalent metal alginate and (b) a salt selected from a monovalent metal salt and an ammonium salt； and a method of producing a freeze-dried monovalent metal alginate composition which comprises the steps of freezing an aqueous solution formed by dissolving at least the component (a) and the component (b), performing first drying, and then performing second drying as desired to reduce a water content to 3% by mass or less. This is a freeze-dried monovalent metal alginate composition with suppressed viscosity decrease with the lapse of time.
