Abstract: Incubation of 16β-Methyl-5α-△⁹⁽¹¹⁾-pregnene-3β, 17α, 21-triol-20-one-3β, 21-diacetate (Ⅰ) with a mixed culture of Nocardia Sp. and Arthrobacter simplex gave 16β-methyl-1,4,9 (11) pregnatriene-17α, 21-dihydroxy-3,20-dione (Ⅱ) (50% yield) together with a small amount of 16β-methyl-△^1,4-pregnadiene-9α, 11α-epoxy-17a, 21-diol-3, 20-dione (Ⅲ).On the other hand, incubation of 17α-methyl-17β-hydroxy-5α-andro-stan-3-one (Ⅳ) with the same mixed culture gave 17α-methyl-17β-hy-droxy-△^1,4-androstadien-3-one (Ⅴ) in 50% yield. However, when a different medium was used for the incubation, the product was 17α-methyl-3,17β-dihydroxy- 9,10-seco-1, 3,5 (10)-androstatrien-9-one (Ⅵ).