Objective:To investigate the role of mitochondria in sodium butyrate-induced apoptosis of ovarian carcinoma cells in vitro.Methods:Human ovarian epithelial cancer 3AO cells were cultured in vitro and treated with sodium butyrate of different concentration for different time. The characters of apoptosis were assessed through light microscopy and DNA ladder analysis. The morphological changes of mitochondria were detected through electron and epifluorescence microscopy. The functional changes of mitochondria and the expression of Bcl-2/Bax protein were analyzed by flow cytometry.Results:As the concentration of sodium butyrate rose to 4mmol/L, the morphologic characters of apoptosis were found by light microscopy, DNA ladder was observed. Under epifluorescence microscope the fluorescence of the control group was stronger than that of the experimental group. Under electron microscope swelled mitochondria was detected. Flow cytometry analysis showed mitochondria transmembrane potentials decreased and there were down-regulate of Bcl-2 protein and up-regulate of the Bax protein(P＜0.05).Conclusion:Sodium butyrate can induce apoptosis of 3AO cells in a time-dose dependent manner. Mitochondrion may play a key role in the procedure of apoptosis of ovarian cancer cells.