Abstract: The erythrocentaurin I and a new lactone II were isolated from Swertia mileensis T.N.Ho et W. L. Shin. in Yunnan (Chinese name: Qing Ye Dan). The yields of I and II were 0.003% (cald. from whole dry herbs). The II was named swermirin. The structure of swermirin was elucidated by means of UV. IR. 1H, 13C NMR and MS. It was assumed to be aglycone really which was obtained through intramolecular rearrangement by hydrolysis of sweroside and swertiamarin as Fig.2.

Key words: erythrocentaurin, swermirin, mieensis