We previously demonstrated that a whole juvenile (2-week-old) mouse ovary transplanted into a syngenic host testis survived and exhibited normal folliculogenesis. The aim of this study was to test whether the graft possessed normal abilities such as ovulation. Whole ovaries were excised from a female transgenic mouse (2-week-old) ubiquitously expressing enhanced green fluorescence protein. The isolated ovary was then transplanted into the testis of a nontransgenic male (2-week-old), in which approximately 80% of the seminiferous tubules had been removed to create enough space for the graft to grow properly. Two months after transplantation, the ovary grafts were isolated from the testis and subjected to histological analysis. Some grafts were subsequently subjected to ovary transplantation to assess the capability of the grafted ovaries to ovulate oocytes. Two months after ovary transplantation, 3 of 8 ovaries grafted under the ovarian capsule successfully ovulated fluorescent oocytes in response to a surge of luteinizing hormone. These results indicate that intratesticular grafting of juvenile ovaries allows functional development of the graft. This system would be helpful for investigating oogenesis /folliculogenesis in ectopic environments as well as for rescuing ovaries with genetic defects.