Objective     To investigate the morphological changes of mitochondria and the expression of bcl-2 in the apoptotic SKOV

3

and 3AO cells induced by arsenic trioxide (As

2

O

3

).      Methods     Light and electron microscopy

flow cytometry analysis

immunofluorescence flow cytometry analysis were used to detect the apoptotic cells

ultrastructural alteration of mitochondria

and the changes of mitochondrial transmembrane potentials (Δψm).      Results     As

2

O

3

i

nduced apoptosis of ovarian cancer cell lines was in a dose dependent manner and various in different cell lines. As

2

O

3

also made a decrease of Δψm in SKOV

3

and 3AO cells in a dose independent fashion. Electron microscopy indicated that the mitochondria showed swollen

balloon-like appearance and outer membrane disrupted 72 h after As

2

O

3

treatment. Expression of bcl-2 was down-regulated in SKOV

3

and 3AO cells after As

2

O

3

treatment.      Conclusion     The reduce of Δψm and down-regulation of bcl-2 may play the key roles in the process of As

2

O

3

-induced apoptosis.