In most mammals, the growth and development of the oocyte and its surrounding somatic cell compartment in the follicle occur in a highly coordinated and mutually dependent manner. Oocytes acquire developmental competence sequentially during follicle growth, finally gaining the ability to undergo complete meiotic and cytoplasmic maturation at the final stage of the preovulatory follicle. Fully-grown immature oocytes are tightly surrounded by compact layers of specialized granulosa cells called cumulus cells that form the cumulus-oocyte complex (COC). After a preovulatory surge of gonadotrophin, the cumulus cells organize a special muco-elastic extracellular matrix (ECM) that requires synthesis and deposition of a large amount of hyaluronan (HA) and HA-binding matrix glycoproteins. Many studies have reported that the formation of the COC matrix mass plays important roles in a variety of reproductive phenomenons: oocyte meiotic maturation with changes of junctional communication and cytoskeletal modification in COC, ovulation, fertilization and early embryo development. Recently, we identified the expressions of HA synthases and the HA receptor, CD44, in the porcine COC matrix. The interaction of HA and CD44 appears to be closely related to gap-junctional communications and meiotic resumption during oocyte maturation. This review describes the recent findings on the regulation and the presumptive mechanism of COC matrix molecules, and physiological features in COC expansion.