A process for isolating the calcium salt of ascorbyl 2-monophosphate from aqueous alkaline reaction mixtures as are obtained on reaction of ascorbic acid with a molar excess of phosphorus oxychloride in the presence of a tertiary amine while maintaining a pH of from 12 to 13 during the reaction by means of an aqueous alkali metal hydroxide solution, which comprisesa) starting from a reaction mixture which has been obtained by reacting ascorbic acid with phosphorus oxychloride in the presence of pyridine while maintaining a pH of from 12 to 13 by means of an aqueous potassium hydroxide solution,b) precipitating, as potassium magnesium phosphate, the phosphate ions which have been formed in this reaction by means of magnesium chloride in amounts of about 1 mol per mol of phosphate ions,c) removing the potassium magnesium phosphate,d) distilling the remaining aqueous solution to remove the pyridine together with part of the water,e) reacting the resulting aqueous solution with calcium chloride andf) isolating the calcium salt of ascorbyl 2-monophosphate which crystallizes thereby, or first distilling the pyridine-water mixture according to step (d) from the reaction mixture obtained in step (a) and thereafter carrying out steps (b), (c), (e) and (f).