To reduce chemotherapy induced gonadotoxicity, co-treatment with gonadotropin releasing hormone against analogue (GnRHa) was tested using rat model. Leuprorelin acetate (Leuplin) with or without cisplatin (CDDP) was given subcutaneously at a dose of 9.4 microg/ml to Wistar strain female rats. The total number of follicles was counted and the maturation of follicles was evaluated at the largest section of the ovary on the 5th and 10th day after administration. Leuplin led the ovary to a resting phase in which primordial follicle occupied 80% of all follicles in only 5 days after administration. The serum E2 level was also down by the 5th day and maintained a low level to the 10th day. In co-treatment with GnRHa and CDDP rats, the primordial follicle occupied 90% of all follicles and the total number of follicles was higher than in CDDP alone rats. This rat model verified that GnRHa co-treatment well minimized CDDP induced gonadotoxocity by desensitization of the ovary. These results were promising for the clinical application introducing GnRHa co-treatment as ovarian protection in cancer chemotherapy in young women.