The quality of oocytes plays a key role in a proper embryo development. In humans, oocytes of poor quality may be the cause of women infertility and an important obstacle in successful in vitro fertilization (IVF). The competence of oocytes depends on numerous processes taking place during the whole oogenesis, but its final steps such as oocyte maturation, seem to be of key importance. In this paper, we overview factors involved in the development of a fully functional female gamete with Xenopus laevis as a major experimental model. Modern approaches, e.g. proteomic analysis, enable the identification of novel proteins involved in oocyte development. EP45, called also Seryp or pNiXa, which belongs to the serpin (serine protease inhibitors) super-family is one of such recently analyzed proteins. This protein seems to be involved in the stimulation of meiotic maturation and embryo development. EP45 is potentially a key factor in correct oocyte development and determining the quality of oocytes.