AbstractThe microbial transformation of mesterolone (=(1α,5α,17β)‐17‐hydroxy‐1‐methylandrostan‐3‐one; 1), by a number of fungi yielded (1α,5α)‐1‐methylandrostane‐3,17‐dione (2), (1α,3β,5α,17β)‐1‐methylandrostane‐3,17‐diol (3), (5α)‐1‐methylandrost‐1‐ene‐3,17‐dione (4), (1α,5α,15α)‐15‐hydroxy‐1‐methylandrostane‐3,17‐dione (5), (1α,5α,6α,17β)‐6,17‐dihydroxy‐1‐methylandrostan‐3‐one (6), (1α,5α,7α,17β)‐7,17‐dihydroxy‐1‐methylandrostan‐3‐one (7), (1α,5α,11α,17β)‐11,17‐dihydroxy‐1‐methylandrostan‐3‐one (8), (1α,5α,15α, 17β)15,17‐dihydroxy‐1‐methylandrostan‐3‐one (9), and (5α,15α,17β)‐15,17‐dihydroxy‐1‐methylandrost‐1‐en‐3‐one (10). Metabolites 5–10 were found to be new compounds. All metabolites, except 2, 3, 6, and 7, exhibited potent anti‐inflammatory activity. The structures of these metabolites were characterized on the basis of spectroscopic studies, and the structure of 5 was also determined by single‐crystal X‐ray‐diffraction analysis.