Abstract: The present study was undertaken to investigate the effects of Luteinizing Hormone (LH, 100 ng mL-1) on bovine oocyte maturation in vitro (Experiment 1) and the relationship between the gap junction and LH (Experiment-2). In experiment 1, cumulus-enclosed oocyte (CO) and Denuded Oocytes (DO) were cultured in the presence or absence of LH. After 42-43 h in vitro culture, nuclear maturation rates which reached the metaphase stage of the second meiotic division (M-ll stage) were observed. In Experiment 2, we evaluated whether the gap junction, formed between cumulus cells and oocytes, was associated with the presence of LH in the maturation medium. The addition of LH to the maturation medium significantly enhanced nuclear maturation of both CO and DO (p<0.05) compared with those oocytes, which were cultured without LH. The addition of 1-heptanol (5 mM), a blocker of coupling in the gap junction, to the maturation medium supplemented with LH significantly inhibited (p<0.05) the number of CO and DO reaching the M-ll stage. These results suggest that the addition of LH to the maturation medium could improve the nuclear maturation of bovine oocytes.