The object of the present invention is a new anhydrous polymorphic crystalline form of sodium hyodeoxycholate (NaHDC) named as form II (FII) and the process for preparing it. Such a process makes it possible to obtain sodium hyodeoxycholate in the anhydrous polymorphic form II (FII), with high chemical and polymorphic purity. The invention also describes the anhydrous polymorphic crystalline forms of NaHDC named as form I (FI) and form III (Fill), the hydrated forms of NaHDC named as SI and SII, crystalline forms of NaHDC, respectively hydrated with four and eight water molecules and the amorphous form.