Various culture media along with some supplements and enrichment materials have been suggested for in vitro maturation. This study aims to investigate the effect of retinoic acid on nuclear maturation of immature mouse oocytes in vitro. Immature oocytes were obtained from 6-8 weeks old NMRI mice, 48 hours after intraperitoneal injection of 7.5 units of PMSG. The collected oocytes were divided into two groups: 1. the control group including the base medium 2. The experimental group including base medium supplemented with 2 μM retinoic acid. 100 oocytes (50 GV oocytes and 50 MI oocytes) were considered for each group. The oocytes of each group were cultured in incubator with 5% CO2 at 37 ºC for 24 hours. The percentage of immature GV and MI oocytes that matured into MII oocytes in the experimental and control groups was (50 & 38) and (38 & 28) respectively. Regarding the maturity of GV and MI oocytes in the experimental group, although the percentage of GV oocytes transformed into MII oocytes was higher than MI oocytes 50% versus 38%, this difference was not statistically significant (PV=0. 1). Results of the present study demonstrated that a higher percentage of immature oocytes in the experimental group matured into MII oocytes. Moreover, GV oocytes are more capable to reach in MII stage compared with MI oocytes in vitro.