Antineoplastic chemotherapy and irradiation affect gonadal function and may lead to infertility. Recovery of gonadal function is frequently observed after conventional chemotherapy in young patients with hematological malignancies, but conditioning regimens before hematopoietic stem cell transplantation result in permanent gonadal failure. Cryopreservation of sperm is effective for male patients, but it becomes difficult even after a single cycle of chemotherapy and therefore should be accomplished before starting chemotherapy. Embryo freezing after in vitro fertilization of harvested oocytes is an established method to preserve fertility in female patients. In addition, harvesting and freezing of unfertilized oocytes is also being evaluated in a clinical study. However, collection of good oocytes after chemotherapy is difficult. In addition, oocyte harvesting is an invasive procedure and may be associated with hemorrhage or infectious complications. Ovarian shielding during total body irradiation allows ovary preservation in most female patients, but this cannot be performed in patients with active malignancies. Strategies for gonadal function preservation should be planned before starting treatment for hematological malignancies.