Abstract: Dehydrogenation of hecogenin acetate (Ⅰ) with "dispersed selenium dioxide" on kieselguhr in chlorobenzene, and in the presence of pyridine, was investigated as a convenient means for the preparation of 9(11)-dehydrohecogenin acetate (Ⅱ). The reaction was carried out at refluxing temperature for 16 hours. Selenium deposited on the kieselguhr could readily be removed from the mixture by simple filtration. Upon working up the filtrate, purified 9(11)-dehydrohecogenin acetate suitable for preparative purposes was obtained in 75-80 per cent of theory. It was then transformed into 5α-pregn-9(11), 16-dien-3β-ol-20-one acetate as a desired intermediate for further synthesis.