Extensive studies have indicated that synaptic plasticity of neurons, including functional and structural plasticity, is intimately related to learning and memory. Recently, a long-term potentiation (LTP) induced by learning was successfully recorded in hippocampal neurons of the trained rats, which lost their retention memory if the late LTP was blocked by a kinase inhibitor. These results show that LTP may be a molecular mechanism underlying memory. Therefore, further studies on synaptic plasticity in the mammalian brain are of significance to revealing molecular mechanisms underlying learning and memory. Furthermore, abnormal morphology, shrinkage and reduced density of dendritic spines and defects in LTP were observed in brains of the patients suffering from mental retardation and neurodegenerative diseases; many mutant genes found from these patients encode component proteins of signal transduction for neuronal plasticity. These studies on synaptic plasticity would certainly promote making the effective prevention and treatment procedures for mental and neurodegenerative diseases. Advances in synaptic plasticity studies and looks into the future of this research field are reviewed.