A new isoguanine glucoside designated saikachinoside A has been isolated from the seeds of Gleditsia japonica. The structure was determined as 7-b-D-glucopyranosyl-3-[(Z)-4-hydroxy-3-methyl-2-butenyl]isoguanine by interpretation of the spectroscopic data and was confirmed by X-ray crystallographic analysis. Saikachinoside A accelerated acetylcholinesterase activity.