OBJECTIVE: To define an appropriate vitrification condition of preantral follicle that yields high survival and to evaluate growth and ovulation rate of mouse follicles during in vitro culture after vitrification. METHODS: Preantral follicles were isolated mechanically from mouse ovaries that were surgically recovered from mice aged 14 days. Retrieved preantral follicles were placed in EG (Ethylene Glycol) for 2, 5, 10 minutes and transferred to EFS-40 (40% EG, 18% Ficoll-70, 0.5 M sucrose) for 0.5, 1, 2 minutes. And then, preantral follicles were placed onto an EM grid and submerged immediately in liquid nitrogen. Thawing was carried out at room temperature. After defining the most appropriate vitrification condition that yields high survival, in vitro growth and ovulation rate of follicles were evaluated. RESULTS: Appropriate vitrification condition that yield high survival rate (83.2+/-2.1%) of preantral follicle was EG for 5 minutes and EFS-40 for 0.5 minutes. In vitro survival rate of the vitrified preantral follicles were 85.5+/-0.5%, 67.9+/-0.8% and 40.2+/-0.5% on day 2, 6 and 10. And in vitro growth of the vitrified preantral follicles were 107.1+/-16.1 micrometer, 117.1+/-18.4 micrometer, 178.4+/-45.6 micrometer and 325.4+/-54.4 micrometer on day 0, 2, 6 and 10. Although in vitro survival rate and growth of vitrified preantral follicles were lower than that of non-vitrified preantral follicles, the patterns of survival and growth were similar in vitrified and non-vitrified preantral follicles. The ovulation rate of antral follicles that was grown from vitrified preantral follicles was 32.6+/-1.2%. CONCLUSION: Vitrified preantral follicles could be grown to antral sizes, and mature oocytes that can be used for IVF-ET programs were produced successfully. These data suggest that cryopreservation of preantral follicle by vitrification can be used for the preservation of the fertility.