The present invention relates to a process for the preparation of hyaluronic acid butyrate, or a salt thereof, acceptable for pharmaceutical or cosmetic use or as a medical device, comprising reacting hyaluronic acid, salified with sodium or another alkali metal, in aqueous solution with butyryl-imidazolide in the presence of sodium carbonate. The present invention also relates to pharmaceutical formulations, cosmetic formulations or medical devices containing the hyaluronic acid sodium salt (HA) butyric esters produced by said process.
