fa Morphometry Morphometry Original Original <strong>Purpose</strong>: The aim of this study was evaluated the effect of &beta; -mercaptoethanol on resumption of meiosis, In vivo maturation of immature mouse oocytes treated with DEHP and embryo development.<br> <strong>Materials and Methods</strong>: NMRI mouse strain (4-6 weeks) were treated daily with 50,&micro;I DEHP Group 1: 121 immature oocytes were matured in MEM-&alpha; medium contain FCS 5%, hCG 7.5 IU/ml, rFsH 100mIU/ml, Group 2: 120 immature oocytes were matured in MEM&alpha; medium contain FCS 5%, hCG 7.5IU/ml, rFsH 100mIU/ml and 100&micro;m &beta;-mercaptoethanol.Control group: 198 immature mouse oocytes recovered from nontreated mouse and were matured in MEM&alpha; medium contain FCS 5%, hCG 7.5IU/ml, rFSH 100mlU/ml. Fertilization and embryo development were done in T6 medium.<br> <strong>Results</strong>: The resumption of meiosis in experimental groups (1&2) were (71%, 79%) respectively. However the resumption of meiosis in experimental groups were significantly different compared to control group (89%) (p<0.05). The In vitro maturation in experimental groups (1,2) were (52%, 68%) respectively. However the in vitro maturation in one group was significantly different compared to control group (75%) (p=0.00) and second group was significantly higher than one experimental group (p<0.01).The embryo number, after 24th insemination in experimental groups (1&2) were (52%, 70%) respectively However the embryo number in first group was significantly lower than the control group (74%) (P<0.05) and second group was significantly higher than the first group (p<0.05).<br> <strong>Conclusion</strong>: The results of this study showed that the &beta;-mercaptoethanol (100&micro;M) inhibited the negative effect of DEHP on In vitro maturation and embryo development. The &beta;-mercaptoethanol has improved the resumption of meiosis, In vito maturation and embryo development. Immature oocyte, In vitro maturation, Mouse, Β-mercaptoethanol, Dehp (Di-(2-ethylhexy) phathalae) 109 116 http://anatomyjournal.ir/browse.php?a_code=A-10-304-104&slc_lang=fa&sid=1 Hosein Imani 10031947532846005413 10031947532846005413 Yes Embryology Department, Royan Institute, Tehran, Iran. Azam Dalman 10031947532846005414 10031947532846005414 No Hoori Sepehri 10031947532846005415 10031947532846005415 No Saeed Kazemi Ashtiani 10031947532846005416 10031947532846005416 No Fatemeh Hasani 10031947532846005417 10031947532846005417 No Mojtaba Reza Zadeh 10031947532846005420 10031947532846005420 No Abdol Hosein Shah Verdi 10031947532846005418 10031947532846005418 No Hosein Bahar Vand 10031947532846005419 10031947532846005419 No