The effects of glutamate (Glu) and glutamine (Gln) on learning and memory of rats and the mechanism involved were examined. Three groups of rats were fed with stock diet (control group), and the diets supplemented with 2% Glu (Glu group) or 2% Gln (Gln group) respectively. Compared with control group, the active avoidance response rats of Gln group in shuttle box test was significantly elevated while the time of passive avoidance response shortened. The contents of brain free amino acids, such as Gln, Glu, aspartic acid and arginine, activity of brain nitric oxide synthase (NOS), Bmax of N-methyl-D-aspartate(NMDA) receptors in hippocampus of Gln group were all increased significantly. Such changes were not observed in Glu group. The results suggested that Gln could improve the learning ability and memory of rats, which might be related to the change of amino acids composition of brain, the synthesis of messenger nitric oxide and the binding capacity of NMDA receptor in hippocampus.