Abstract: Objective To observe the changes of mitochondria ultramicrostructure of mucinous cystadenocarcinoma(MC) and serous cystadenocarcinoma(SC) and to determine the stereological characteristic of the mitochondria of ovarian carcinoma cells and to investigate the value in clinical diagnosis of two cystadenocarcinoma Methods The ultramicrostructure changes of mitochondrion were observed with electronic microscope and the interrelation of volume density（Vvm）, surface density（Sv，μm－1）and membrane surface density （Rsv, μm－1）of mitochondria of the cells in ovarian carcinoma were studied and compared with the normal control. Results Electron microscope reveals that the mitochondria swelling and cristae disorganizing were seen in ovarian carcinoma. The Vv and Sv of mitochondria of the MC cells were mitochondria increased obviously（0.891±0.04，P＜0.05）。The Vv and Sv of mitochondria of the SC cells were increased markedly (0.267 ± 0.12 and 0.122 ± 0.06, P＜0.01), while the its Rsv of mitochondria was declined obviously（0.584 ± 0.49，P＜0.05）Conclusion There are obviously changes in the mitochondria of two types ovarian carcinoma.The number of mitochondria in former type is decreased, while the that of the latter is increased.