Abstract: This invention discloses a process for producing 2,6-bis (4-hydroxy-3,5-dimethoxyphenyl)-3,7-dioxabicyclo [3.3.0] octane, i.e. syringaresinol and stereo-isomers thereof, from plants which contain lignin with syringyl unit. The process comprises heating plant under pressure in hydrous condition, and then quickly discharging them therefrom into an environment at atmospheric pressure so as to explode into pieces and subjecting the fine pieces to extraction with organic solvent such as methanol and acetone or an alkaline solution such as sodium hydroxide and purification. Syringaresinols are useful like ginseng as a tonic.