Incubation of 16, 17α-oxido-5α and 5β-pregnane-3β-ol-zo-one (1 and 2) with Nocardia sp.afforded four compounds (4, 6, 8, 7 and 8, 6, 6, 7)respectively, among which 16,17α-oxido-⊿⁴-pregnene-3, 20-dione (6) was the major product, while separate incubation of 1 and 2 with Arthrobdctor simplex both afforded only two unsatureted compounds (16 and 16)having 20-hydroxy group, in which 16, 17α-oxido-⊿^1,4-pregnadiene-20α-ol-3, 20-dione (16) was the major product.Incubation of 16, 17α-oxido-16β-methyl-5α-⊿⁹⁽¹¹⁾-pregnane-3,8-01-20-one (8) with Nocardid sp.gave three oompounds(12,18,14),in which 16, 17α-oxido-16β-methyl-⊿^4,9(11)-pregnadiene-3, 20-dione (18) was the major product.It seemed that 5α and 5β steroids were mainly dehydrogenated at C_4,5 by Nocardia sp.and at C_1,2 and C_4,5 by Arthrobactor simplex.