［Abstract］ Objective To investigate the developmental characteristics of dendritic spines in mouse hippocampal CA1 pyramidal neurons by analysing the spine density and morphological changes. Methods Fifty mice were collected at postnatal days (P) 0, 5, 10, 20 and 30, 10 mice for each age. DiI diolistic labeling with gene gun was performed to observe dendritic spines development in mouse hippocampal CA1 pyramidal neurons. High quality labeled neurons were examined and photographed under a confocal microscope, whereas the ultrastructure of spines was observed under a transmission electron microscope. Results Dendritic spines changed their morphology and density with mouse development in response to neuronal activity. The smooth endoplasmic reticulum and spine apparatus in dendritic spines of hippocampal CA1 were observed with electron microscopy analysis, which might be involved in the regulation of plasticity at individual synapses.Conclusion The development of dendritic spines may be closely related to synaptogenesis and the