In the present study, we assessed the effects of β-mercaptoethanol (β-ME) added to in vitro maturation (IVM) medium on the development of resultant embryos derived from in vitro fertilization (IVF) of oocytes, the number of cumulus cells, and ATP content of bovine oocytes. Furthermore, we counted the number of cells of the blastocysts derived from IVF of oocytes matured in media with or without 100 μM β-ME. When β-ME was added into the medium of IVM at concentrations of 0, 10, 50, 100 and 500 μM, the rate of embryonic development to the blastocyst stage of resultant embryos increased significantly (P<0.05) in the 100 μM group compared to the 0 μM (control) group. Although β-ME was added to media with the same concentrations (0, 10, 50, 100 and 500 μM) for the embryonic culture following in vitro fertilization of oocytes matured without β-ME, the rates of embryonic development to the blastocyst stage decreased in a concentration-dependent manner. The number of cumulus cells attached to the oocytes matured in media with 100 μM β-ME was significantly greater (P<0.05) than that in the 0 μM group. There was no difference between ATP contents of cumulus cell-enclosed oocytes (CO) matured with or without 100 μM β-ME. In contrast, the ATP content of cumulus cell-denuded oocytes after maturation in media supplemented with 100 μM β-ME was significantly lower (P<0.05) than that of the 0 μM-treated group. In addition, the average cell number of blastocysts in the 100 μM β-ME group was significantly greater (P<0.05) than that of the 0 μM group. These results suggest that β-ME may increase both the numbers of cumulus cells attached to oocytes and the cell numbers of blastocysts derived from in vitro fertilization by influencing the ATP metabolism of bovine oocytes during IVM.