In order to increase the pregnancy rate by means of cryopreservation of the excess oocytes in IVF-ET program, the survival rate of the frozen-thawed oocytes of mouse was examined according to the stages of maturation, cryoprotectants and their treatment. The results were summarized as follows. First, during the continuous treatment with cryoprotectant media, the survival rate of oocytes was higher in DMSO than in PROH, and higher at low temperature($4^{circ}C$) than at room temperature($25^{circ}C$). Second, as regard with the maturation of immature(GV-intact) oocytes after treatment with cryoprotectant media, the rate of maturation in DMSO-treated group(52%) was higher than in PROH-treated group(35%). Third, according to the treatment of cryoprotectant media, the survival rate of frozen-thawed oocytes in DMSO-treated group (45%) was higher than in PROH-treated group(29%), and that of oocytes in DMSO 4-step treated group was higher than any other groups. Finally, in the post-thaw oocytes frozen at various stage of maturation, the survival rate of immature oocytes with GV was the highest in all groups. These results suggest that in the cryopreservation of mouse oocytes, DMSO was better than PROH as cryoprotectant, in treatment of cryprotectant the multi-step treatment was better than single-step, and the post-thaw survival rate of oocytes was closely related to the maturity of oocytes. It is assumed that the highest survival rate of mouse oocytes with GV is due to the stability of the structures in nucleus and intracelluar organelles, and of physiological function.