The present invention provides processes for preparing soluble salts of inositol phosphate characterized by a low level of impurities. Processes for preparing soluble salts (e.g., alkali-metal or ammonium) of inositol phosphates (e.g., hexasodium or dodecasodium salts), and of inositol hexaphosphate in particular (e.g., Na6IP6 and Na12IP6), are described. Also provided are pharmaceutical compositions, methods of use, combination treatments, kits, and articles of manufacture comprising soluble salts of inositol phosphates prepared according to the method of the invention.