Abstract: A pentacyclic triterpenoidal lactone, named triptotriterpenoidal lactone A, with a molecular formula of C_30 H_46 0_3 and m.p. of 322.5—326.5'C, was isolated from the bark root of Tripterygium wilfordii Hook. f. The lactone obtained is a new constituent and its acetyl derivative were subjected to IR, NMR and MS analysis and it's structure has been determined.