The present application provides an improved process for the preparation of sugammadex by reacting a salt of 3-mercapto propionic acid with 6-per-deoxy-6-per-halo-γ-cyclodextrin in a suitable organic solvent. This application also provides crystalline form of a salt of 3-mercapto propionic acid, preferably di sodium salt of 3-mercapto propionic acid and its use for the preparation of sugammadex, whereas formula (I) shows the sodium salt of sugammadex.