Based on NOE experiments, the structure of naphthodipyranodione from Gentianaceae plants was revised to 1,2-dihydro-4H,6H,8H-naphto[1,2-d:4,5- c'd']dipyrano-4,8-dione. Naphthodipyranodione was assumed to be formed by the degradation of gentiopicroside by enzymatic hydrolysis at low water -concentration. The degradation pathway was a unique domino-reaction triggered by enzymatic hydrolysis. Naphthodipyranodione may become an index compound for the drying and/or fermenting procedure of Gentian root.