Objective：To observe the apoptosis of developi ng spinal cord and spinal ganglion in the mouse embryo. Methods：The density of apoptotic cell(DAC) of the brachial plexus

thoracic and lumbar plexus of spinal cord (SC)and spinal ganglion (SG)in the serial sections of fetal ICR mice aged 12～15.5 days was measured with the stereological method.The apo ptosis was also showed with TUNEL method in some sections for contrast.Re sults：The apoptotic cells with karyorrhexis can be seen in SC and SG of fetal mice.The apoptotic cells of SC are mainly located in the basal plate

but rarely in the alar plate.The statistical results showed that the peak values of DAC in the three sections of SC all appeared on day 14

P＜0.01; the peak value of DAC in the brachial plexus of SC was higher than the other two sections

P＜0.0 5

except day 15.The peak values of DAC in the thoracic and lumbar plexus of SG all appeared on day 15

P＜0.01;the DAC of brachial plexus was not clear.Conclusion ：The apoptotic cells in SC and SG of fetal mice aged 12～15.5 days were mainly found in the basal plate of SC and the SG.The pea k values of DAC in SC were one day earlier than in SG.The peak values of DAC in the three sections of SC and SG may be related with their tissue-differeniation.