The bi-directional communication between mammalian oocytes and their surrounding granulosa cells has been shown to be crucial for ovarian follicular development. Studies on molecules derived from the oocytes, such as growth differentiation factor-9 (GDF-9) and bone morphogenetic protein-15 (BMP-15), have attracted great interest during the past decade, and it is common knowledge nowadays that these molecules participate in the bi-directional dialogue between the oocytes and their surrounding granulosa cells as well as follicular development. However, signaling molecules and pathways inside mammalian oocytes that control oocyte growth and early development of ovarian follicles, which may be monitored by factors produced by granulosa cells, have not been studied extensively. Based on our own data as well as ovarian phenotypes observed in several gene modified mice strains that were generated for studies of signal transduction, immunology and cancer, the current review focuses on the key features of the activation of oocyte phosphatidylinositol 3 kinase (PI3 kinase) pathway and its possible roles during mammalian oocyte growth and follicular development. We propose that the cascade from the granulosa cell-produced stem cell factor (SCF) to the oocyte surface SCF receptor Kit, and to the oocyte PI3 kinase pathway, may play an important role in the regulation of growth rate of mammalian oocytes, as well as in the activation and development of ovarian follicles.