The biotransformation of vulgarin(1), an eudesmanolides-type sesquiterpene lactone obtained fromArtemisia judaica, by the microorganism,Aspergillus niger, was carried out to give three more polar metabolites; 1-epi-tetrahydrovulgarin (1α,4α-dihydroxy-5αH,6,11βH-eudesman-6,12-olide(2), 20% yield, 1α,4α-dihydroxyeudesm-2-en-5αH,6,11βH-6,12-olide(3a), 10% yield, and C-1 epimeric mixture(3a, b), 4% yield, in a ratio of 4:1,3a/3b. The structures of vulgarin and its metabolites were elucidated by 1 and 2D NMR spectroscopy in conjunction with HRESIMS. Metabolites(3a)and(3b)are epimers, and they are reported here for the first time as new metabolites obtained by biotransformation by selective reduction at C-1. Vulgarin and its metabolites were evaluated as anti-inflammatory agents using the human cyclooxygenase (COX) inhibitory assay. The obtained data showed that(1)exhibited a good preferential inhibitory activity towards COX-2 (IC50 = 07.21 ± 0.10) and had a moderate effect on COX-1 (IC50 = 11.32 ± 0.24). Meanwhile, its metabolite(3a)retained a selective inhibitory activity against COX-1 (IC50 = 15.70 ± 0.51). In conclusion, the results of this study revealed the necessity of the presence α, β unsaturated carbonyl group in(1)for better COX-2 inhibitory activity. On the other hand, the selectivity of(1)as COX-1 inhibitor may be enhanced via the reduction of C-1 carbonyl group.