Background: Rhizoma dioscoreae nipponicae is a perennial herb and its roots have been widely used in Traditional Chinese Medicine (TCM). Objective: To develop and optimize the extraction and hydrolysis technology of diosgenin from Rhizoma dioscoreae nipponicae. Materials and Methods: 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate ([PSMIM]HSO4), as a kind of functional ionic liquid, replaced inorganic acid, and was used in a one-step ultrasonic extraction and hydrolysis for the preparation of diosgenin (the aglycone of dioscin and an important precursor chemical in the pharmaceutical industry) from Rhizoma dioscoreae nipponicae, for the first time. The effects of various factors were evaluated. The obtained product was studied using high performance liquid chromatography (HPLC). Results: About 6.35 mg of diosgenin could be obtained from 2.0 g of raw material. Reusability and recycling of the ionic liquid were validated with fairly good results. The ionic liquid solution was reused four times, and the final extraction efficiency only decreased by 5%. Conclusion: In virtue of the obvious advantages of the green extraction and catalytic solvent, with further study, it is believed that this new one-step preparative method promises to replace the traditional methods.