Plasmalogens (Pls) are unique glycerophospholipids containing a vinyl ether bond at the sn-1 position of the glycerol backbone, which are not only structural membrane components and reservoirs for second messengers, but they are also involved in membrane fusion, ion transport and cholesterol efflux. It has been well known that our brain, especially the hippocampus, contains a large amount of ethanolamine plasmalogens (EthPls) and previous reports in the Alzheimer's disease (AD) patients have shown that Pls are reduced in the brain tissues suggesting a role of Pls in the memory. We therefore, performed memory test with the mice that contained reduced Pls in the hippocampus. To knock down the Pls in the hippocampus, we have designed short hairpin RNAs (sh-RNAs) based on lentivirus vectors against the two major enzymes GNPAT (glyceronephosphate O-acyltransferase) and AGPS (alkylglyceronephosphate synthase) necessary for the de novo synthesis of Pls. These lentiviruses effectively reduced the expression of GNPAT and AGPS in the cells and also in the hippocampal tissues. For the behavioral study, we injected the lentiviruses at the dose of (5X105 transduction unit) into the hippocampus directly by stereotaxic instrument. Morris water navigation task showed a significant reduction in the memory from first week to the 5th weeks of the injection in Pls knock-down mice. In addition we found a significant reduction in the expression of brain derived neurotrophic factor (BDNF) and its target genes Synapsin-1 and Synaptotagmin-1 in the Pls knock-down hippocampus as well as Neuro-2A cell line. Furthermore, the mice receiving Pls-containing diet for 6 weeks showed increase Pls content in hippocampus and memory enhancement in Morris water maze test, which was blocked by knock-down of BDNF gene. Our present study confirms for the first time that the endogenous Pls in the hippocampus are very important to maintain our memory via regulating the expression of BDNF and its related genes.