Introduction: The purpose of this study was to evaluated the effect of β-mercaptoethanol on resumption of meiosis, in vitro maturation of immature mouse oocytes and resulting embryo development with and without BSO (DL-Buthionine sulfoximine). Material and Methods: Germinal vasicle (GV) were recovered from 6-8 weeks old NMRI ovaries and cultured in maturation medium in MEMα supplemented with 7.5IU/ml hCG, 100mIU/ml rhFSH, 5% FCS (control group) and adding 100μm β-mercaptoethanol (group 1) or with 5mM BSO + 100μm β-mercaptoethanol (group 2) for 24h. The matured oocytes then were fertilized and cultured for 5 days. Fertilization and development were accomplished in T6 medium. Results: The percentage of GV oocytes reaching to metaphase I (or undergo GVBD) were 78.5%, 85%, 86% in control group, group 1 and group 2 respectively, that no significant difference was detected between groups. The proportion of oocytes that progressed to the metaphase II (MII) stage was minimum within 5mM BSO group (group 2) and maximum within β-mercaptoetanol group (group 1) with significant difference comparing with control and each other (P≤0.05). The percentage of embryos reaching to morula stage within β-mercaptoetanol group was significantly higher than the control group (5% and 12.2% respectively). None of oocytes treated with BSO could pass the 8 cell stage. Conclusion: β-mercaptoetanol enhances IVM and improves embryo development. While adding BSO into the maturation medium even with β-mercaptoetanol decreases maturation and declines the embryo development.