Corticosteroid 9,11β-epoxides are key intermediates in the preparation of pharmaceutically important compounds such as betamethasone, mometasone, beclomethasone, and dexamethasone. A new process for the 9,11β-epoxide was developed using a PCl 5 -mediated regioselective dehydration of 11r-hydroxysteroid to form the corresponding ∆ 9,11 double bond. The olefin is then converted into 9r,11β-bromoformate by treatment with 1,3-dibromo-5, 5-dimethyl hydantoin (DBH) in DMF and subsequently cyclized to produce the desired 9,11β-epoxide upon treatment with NaOH. Major process-related impurities such as 21-OH-∆ 9,11 -triene, 21-OH-∆ 11,12 -triene, 21-Cl-∆ 9,11 -triene, and β-epoxide-21-cathylate as well as 11β-Cl are all eliminated or minimized. This new process has been implemented in our manufacturing facility in full-scale production and proved to raise the overall yield and the quality of the product dramatically compared to the existing process.