Riboflavin has been converted to phosphated ester, riboflavin 5 cphosphate sodium, by the phosphorylation of riboflavin with pyro-phosphoric acid in three steps reaction. The yield is 80.5 % of the theoretical value and assay shows 84.5 % purity in the product. The water solubility has been increased to 112 mg/ml at 27°C.