Two new metabolites were isolated from the biotransformation reaction of parthenin by Beauveria bassiana ATCC 7159 along with the known naturally occurring sesquiterpene lactones hymenolin and dihydrocoronopilin. The new metabolites: are 3beta,4beta,6beta-trihydroxy-10alphaH,11alpha-methyl-ambrosa-1 -en-12-oic acid-gamma-lactone and 3alpha,6beta-dihydroxy-4beta-hydroperoxy-10alphaH, 11alpha-methyl-ambrosa-1-en-12-oic acid-gamma-lactone. The structure elucidation of these compounds was achieved by different spectroscopic methods.