A new isoflavanone 2′,2,5-trimethoxy-6,7-methylenedioxyisoflavanone was isolated from the aerial parts of Iresine herbstii, together with isoflavone tlatlancuayin (2′,5-dimethoxy-6,7-methylenedioxyisoflavone). The structure was identified using spectroscopic analysis. This is the first description of a methoxy group occurrence at position 2 of the isoflavanone skeleton. Both isolated compounds were tested for α-glucosidase inhibitory activity, but showed only a low effect compared to hyperoside.