We investigated the in vitro inhibitory acetylcholinesterase (AChE) activities and in vivo ameliorating effects on scopolamine-induced memory impairment of nine iridoid glycosides, namely, geniposide (1), genipin gentiobioside (2), gardenoside (3), scandoside methyl ester (4), deacetylasperulosidic acid methyl ester (5), 6-O-methyldeacetylasperulosidic acid methyl ester (6), geniposidic acid (7), gardoside (8), and shanzhiside (9), isolated from the fruits of Gardenia jasminoides (edible gardenia). Contrary to preliminary studies, genipin gentiobioside (2) exhibited the greatest anti-AChE activity (60.23 +/- 2.12%) and antiamnesic effects (ca. 2-fold enhancement vs. the untreated control) using a passive avoidance task system, which is comparable to tacrine. Structure activity relationships are suggested, which would be useful for identifying candidate compounds for the treatment of memory dysfunction.