Objective: To investigate effects of cryoprotectant and cryopreservation on the chromosome of the human immature oocytes. Design: Intact cumulus-enclosed immature oocytes were collected from unstimulated ovaries and divided into three groups, such as no treatment as control (group 1), only 1,2-propanediol (PROH)-treated (group 2), and cryopreserved oocytes (group 3). Oocytes in group 1, 2, and survived oocytes after cryopreservation in group 3 were cultured for 48 hours. Setting: Infertility Medical Center at the CHA General Hospital, Seoul, Korea. Patients: Oocytes were obtained from Patients undergoing gynecological surgery. Main Outcome Measures: Maturation rate, abnormality in chromosomes by fluorescence in situ hybridization (FISH). Results: There was no effect of PROH only treatment on the chromosomal abnormalities in group 2 compared to control oocytes (41.4% and 31.8%, respectively). Whereas significantly increased abnormalities in chromosome (77.8%) were found in group 3. Conclusions: Human oocytes matured in vitro after cryopreservation at the germinal vesicle (GV) stage showed increased incidence of chromosomal abnormalities. These abnormalities may impair the capacity for further development of the embryos derived from frozen-thawed oocytes.