The effects of β-hydroxybutyrate (BHB) added to a modified NCSU37 medium during in vitro maturation (IVM) on nuclear maturation, and ATP and glutathione (GSH) contents of porcine oocytes were investigated. Nuclear maturation up to the metaphase stage of the second meiotic division (the M-II stage) of cumulus cell-enclosed oocytes (COs) matured with various concentrations (0.0, 2.3, 3.1, 3.9 and 4.7 mM) of BHB was observed. The nuclear maturation rate of the oocytes of the 3.1 mM group was significantly higher (P < 0.05) than that of the control (0.0 mM) group. Both the ATP and GSH contents of the oocytes matured with or without 3.1 mM BHB and removed from cumulus cells after IVM were not significantly different. These results indicate that 3.1 mM BHB added to the maturation medium may stimulate the nuclear maturation of porcine oocytes without changing their ATP and GSH contents.