Abstract: This paper describes the hydroxybromination of 5α-androst-2-en-17-one(Ⅱ).When 2β-hydroxy-3α-bromo-5α-androstan-17-one(Ⅳ) is prepared from 5α-androst-2-en-17-one(Ⅱ) by NBS and 60% HC1O4 in dioxane, three by—products(Ⅳa, Ⅳb and ⅣC ) are produced and separated by chromatographic column on silica gel. Their spectral data, physicochemical properties and derivatives, demonstrate that the structures are 2β,3α-dibromo-5α-androstan-17-one(Ⅳa), 3α-bromo-4β—hydroxy-5α-androstan-17-one(Ⅳb) and 3α-hydroxy-4β-bromo-5α-androstan-17-one(Ⅳc) respectively.According to the above experimental results the △3 —isomer Ⅲ may also be formed, if Ⅱis prepared from the tosylate I by thermal elimination with collidine.