Objective       To study the expression of Bcl-2 and Bax in developing hippocampus of mice.      Methods       Expression of Bcl-2 and Bax in developing hippocampus of mice was detected by immunohistochemistry and image analysis

respectively.      Results       Bcl-2 immunohistochemistry showed a small number of Bcl-2 positive cells in CA1 area on embyronic (E) day 16 and in hippocampus on E d 18

especially in pyramidal layer

which became intensive and then sparse in hippocampus on postnatal (P) days 1-21

especially in CA3 area on P7 day

which then remained stable from P28 day. The average optical density (AOD) for Bcl-2 positively expressed cells in pyramidal layer increased and reached its peak on P7 day and then decreased（P0.01）

which remained stable from P28 day（P0.05）. The findings in Bax immunohistochemistry were similar to those in Bcl-2 immunohistochemistry. The Bcl-2 and Bax ratio decreased gradually from E18 day to P1 d（P0.01）and then remained stable（P0.05）.      Conclusion      Bcl-2 and Bax are highly expressed in embryo and hippocampus of early postnatal mice and reached their peak on P1 day. However

they are lowly expressed in adult and aged mice.