Prostaglandins (PGs) are implicated in various physiological and pathological functions because of their vasoactive, mitogenic, and differentiating properties. PGs have long been known to participate in various female reproductive functions. The cyclooxygenase (COX) isozymes, COX-1 and COX2, are the rate-limiting enzymes of PGs. Gene targeting studies have revealed that COX-2, but not COX-1, derived PGs are essential for ovulation, fertilization, implantation, and decidualization. However, the roles of PGs in oocyte maturation remain controversial. We have clarified that COX-2-deficient mice have defective oocyte meiotic and cytoplasmic maturation associated with defective cumulus expansion in vivo and in vitro. Lack of COX-2-derived PGE2 leads to impaired cumulus cell-oocyte interactions, which are critical for the production of fertilization-competent oocytes. This review summarizes the published data regarding the roles of PGs in oocyte maturation especially in gene targeting studies.