Introduction of a hydroxyl group at the C-8β position of l-α-santonin (1) was achieved by chemical and microbiological methods. The chemical transformation of 1 was accomplished via the 8β-hydroxy compound (5b) derived from 3, 8-dioxoeudesm-1, 4, 6-triene (4). The enol acetate 7 of the 8β, 12-olide (6) derived from 5b was treated with hydrogen peroxide in formic acid, giving the 6α-hydroxy-8β, 12-olide (8). Compound 8 was converted into 8-epiartemisin (2b) by hydrolysis of the ester group followed by lactonization.The microbiological transformation of 1 into 2b was performed by the use of Aspergillus sp. MIL 5024.