Swertiajaponin, C₂₂H₂₂O₁₁, m.p. 265° (decomp.), was newly isolated from the whole herb of Swertia japonica MAKINO (Gentianaceae), and identified as 6-C-β-p-glucopyranosyl luteolin-7-methylether. Iso-swertiajaponin, C₂₂H₂₂O₁₁, m.p. 258~261° (decomp.) was obtained by the acid treatment of swertiajaponin, and formulated as 8–C–β–p–glucopyranosylluteolin–7–methylether. At the same time, it was found that they were interconvertible into each other by boiling with mineral acids, reminiscent of the interrelationship between swertisin and isoswertisin.