Ovulation is a critical process for female reproduction. In the majority of mammals, oocyte maturation occurs during ovulation when the oocyte resume meiosis and advance to metaphase II. In response to the preovulatory gonadotropin surge, cumulus cells produce hyaluronic acid that binds to maturing oocytes. Cumulus expansion occurs when hyaluronic acid gets hydrated, the gaps between cumulus cells expand, and the cells become embedded in a sticky, mucified matrix. Cumulus expansion is one of several necessary processes in preovulatory follicles for ovulation to occur. If either oocyte maturation or cumulus expansion is inhibited, the ovulation rate is drastically decreased. Hence, both of these processes are good targets for novel contraceptive development. Previous studies have demonstrated the presence of a voltage-activated K+ current with a large conductance in unfertilized eggs. However, the role of potassium channels in oocyte maturation and cumulus expansion is largely unexplored. In this study, ​the role of K+ channels in​ oocyte maturation and cumulus cell expansion has been investigated. Potassium channel inhibitors such as TEAC, valinomycin, and PA-6 were found to reduce cumulus growth in oocytes. To examine the effect of specific potassium transport inhibitors and activators, their ability to inhibit morphological ​expansion and the expression of expansion genes (HAS2, PTGS2​, PTX3, and TNFAIP6) were assessed. The three potassium channel inhibitors were shown to significantly reduce expansion transcript expression. Our data demonstrate that potassium channels ​play a crucial role in​ cumulus expansion and oocyte maturation and that these channels might be a target for the development of new contraceptives.