fa Morphometry Morphometry Original Original <strong>Purpose</strong>: This Study evaluated the resumption of meiosis, in vitro maturtion and department of immature mouse oocytes with b- mercaptothanol.<br> <strong>Materials and methods</strong>: Immature oocytes were recovered from NMRI mouse strain (4-6 weeks) in different 4 experiments groups: the control group, the oocytes were matured in MEM-a+ medium containing + FCS 55%; group 1: the oocytes were matured in MEM- a medium containing + FCS 5% and b-mercaptoethanol; group 2: the oocytes were matured in MEM-a+ FCS 5%, rFSH 100mIU and group 3: the oocytes were mature in MEM- a medium containing, FCS 5%, hCG 7.5IU, rFSH100mIU, b-mer-captoethanol 100 mm. Fertilization and embryo development were done in T6 medium.<br> <strong>Results</strong>: There were significant differences on in vitro maturation between control group than the group 1 and group 3 (p=0.01, p=0.007) and resumption of miosis between control group than the group 1 and group 3 (p=0.009, p=0.001).The rates of the resumpsion of meiosis in experimental groups were 74.20 (control), 82.71 (group 1), 84.49 (group 2) and 85.49% (group 3), In vitro maturation also increased significantly with (3-mercapthoethanol (group 1=69.49%, group 3=70.22%).The embryo formation on the fourth day in group 1 than the control group, group 2, group 3 (p=0.001, p=0.000,p=0.000) increased more significantly than that in the other groups.<br> <strong>Conclusion</strong>: The results of this study showed that b-mer-captoethanol (100 mm)has an effect on in vitro maturation and resumption of meiosis of mouse oocytes and improves embryo development. Immature oocyte, Beta-mercaptoethanol, Mouse 37 45 http://anatomyjournal.ir/browse.php?a_code=A-10-304-56&slc_lang=fa&sid=1 Hosein Imani 10031947532846006780 10031947532846006780 Yes Embryology Department, Royan Institute, Tehran, Iran. Fatemeh Hasani 10031947532846006781 10031947532846006781 No Seyyed Ali Haeri Rouhani 10031947532846006782 10031947532846006782 No Mohammad Hosein Nasr Esfahani 10031947532846006783 10031947532846006783 No Azam Dalman 10031947532846006784 10031947532846006784 No Mojtaba Reza Zadeh 10031947532846006785 10031947532846006785 No Saeed Kazemi Ashtiani 10031947532846006786 10031947532846006786 No Abdolhosein Shahverdi 10031947532846006787 10031947532846006787 No Hosein Bahar Vand 10031947532846006788 10031947532846006788 No