A new sesquiterpenoid lactone (I), neoaristolactone, was isolated from the root of Aristolochia mollissima Hance. This crystal belongs to the triclinic system, space group is P1, with a = 0.6275(3) nm, b = 0.8075(4) nm, c = 1.3622(6) nm; a = 88.78(4)? b = 91.44(4)? g = 105.20(4)? Z = 2.3107, reflections were collected on a Rigaku AFC5R diffractometer with monochromatized MoKa radiation and corrected for Lp factors and empirical absorption, of which 1468 observed reflections were used in structural determination The structure was refined to a final R value of 0.079 by the full-matrix least-squares.

Key words: CRYSTAL STRUCTURE DETERMINATION, LACTONES, ARISTOLOCHIA, ANTITUMOR DRUGS, SESQUITERPENE