Scanning electrochemical microscopy (SECM) is a non-invasive and sensitive technique for measuring cellular respiration. In this paper, we review the SECM technique, to establish it as an accurate method for measuring the respiratory activity of single cumulus-oocyte complexes (COCs) and oocytes in animals as well as in humans. Oxygen consumption rates of COCs are influenced by the surrounding cumulus volume and the mitochondrial activity of the cumulus cells. An increase in the oxygen consumption rate was found in bovine oocytes, whereas the oxygen consumption of human oocytes tends to decrease during in vitro maturation (IVM). To analyze the metabolic activity of mitochondrial respiration, ATP content and mitochondrial distribution in bovine oocytes have been examined. An electron microscopic study confirmed mitochondrial reorganization in bovine oocytes during oocyte maturation. These results show that the respiratory activity of oocytes changes with maturation status during IVM and mitochondrial reorganization may partly influence respiratory activity. The SECM procedure is therefore a useful technique for evaluating the metabolic activity and quality of oocytes and cumulus cells in the IVM process.