Abstract: Arteannuin B (I) was converted to hydroxy lactones (Ⅶ, Ⅷ) by amixture of formic acid and sulfuric acid. Compound Ⅵ and Compound Ⅶ both showedactivity against leukemia P 388 cell in vitro. The rate of growth inhibition were 97.5%and 11.8% for(Ⅵ)and 80% and 52.6% for(Ⅶ)at the concentration of 10 and 1μg/mlrespectively. It seems that the antileukemia activity of 6- membered lactone is higher thanthat of 5- membered and the methylene group is necessary for the antileukemia activity.