Provided are: a freeze dried composition which contains (a) a monovalent metal salt of alginic acid and (b) a salt selected from among monovalent metal salts and ammonium salts and a method for producing a freeze dried composition of a monovalent metal salt of alginic acid which comprises a step wherein an aqueous solution in which at least the above described component (a) and component (b) are dissolved is frozen and primarily dried and then if desired is dried secondarily so that the moisture content thereof becomes 3% by mass or less. The present invention is a freeze dried composition of a monovalent metal salt of alginic acid which is suppressed in decrease of viscosity over time.
