Debilosides A -C (1 -3), three new megastigmane glucosides, were isolated from the whole plant of Equisetum debile, together with the four known constituents blumenol A, corchoinoside C, sammangaoside A, and (3S,5R,6R,7E,9S)-9-[(b-D-glucopyranosyl)oxy]megastigm-7-ene-3,5,6-triol (4). Their structures were elucidated on the basis of in-depth spectroscopic analyses including 2D-NMR techniques. Introduction. -Equisetum debile ROXB. (Equisetaceae), distributed widely in Southeast China, has a long history as a Chinese folk medicine for the treatment of acute hepatitis, urethritis, and conjunctivitis, as well as against diarrhea [1]. To our knowledge, no previous study on the chemical constituents of this plant was reported. In the course of our phytochemical investigations of E. debile, we now report the isolation and characterization of three new megastigmane glucosides, debilosides A -C (1 -3), and of four known norisoprenoids, blumenol A [2], corchoinoside C [3], sammangaoside A [4], and (3S,5R,6R,7E,9S)-9-[(b-D-glucopyranosyl)oxy]megastigm-7ene-3,5,6-triol (4) [5]. Results and Discussion. -Debiloside A (1) was obtained as a white, amorphous powder. Its ESI mass spectrum displayed the [M + H] + ion peak at m/z 387, in accord with the molecular formula C 19 H 30 O 8 . The 1 H-and 13 C-NMR spectra of 1 (Table) indicated a b-glucopyranosyl (Glc) unit (d(C) 101.8, 78.8, 78.6, 75.5, 72.2, 63.3; d(H) 4.27 (d, J = 8.0 Hz, 1 H)). The aglycone part of the NMR spectra indicated three Me groups (d(H) 1.01 (s); 1.03 (s); 1.28 (d, J = 6.6 Hz)), a tertiary CH 2 OH group (d(H) 4.18,