<p>Background: This study aimed to investigate the maturation and fertilization rates of immature mouse oocytes using Embryonic Stem Cell Conditioned Medium (ESCM).<br /> Methods: Germinal Vesicle (GV) stage oocytes were observed in 120 NMRI mice, aged 4-6 weeks. GV oocytes with or without cumulus cells were subjected to IVM in either ESCM, Embryonic Stem Cell Growth Medium (ESGM), or &alpha;-minimum essential medium (&alpha;-MEM). After recording the Metaphase II (MII) oocyte maturation rate, the oocytes were fertilized<em> in vitro</em>. The fertilization success rate was recorded after 24 <em>hr. </em>The embryos were maintained in potassium Simplex Optimization Medium (KSOM) for 96 <em>hr</em> and allowed to grow until the blastocyst stage. After recording developmental competence, they were transferred into the uteri of pseudopregnant mice and their birth rates were recorded.<br /> Results: No significant difference existed between the maturation rates in &alpha;-MEM (68.18%) and ESCM (64.67%; p&gt;0.05), whereas this rate was significantly higher for both &alpha;-MEM and ESCM compared to ESGM (32.22%; p&lt;0.05). A significant difference in IVF success rate existed for oocytes grown in &alpha;-MEM (69.44%), ESCM (61.53%), and ESGM (0%). A significantly higher developmental competence was observed at the blastocyst stage for oocytes grown in &alpha;-MEM (51.2%) compared to ESCM (35%; p&lt;0.05). 17 days after embryo transfer into the uteri of pseudopregnant mice, there was a nonsignficant (p&gt;0.05), similar birth rate between &alpha;-MEM and ESCM (47 <em>vs</em>. 40%).<br /> Conclusion: ESCM is an effective medium for preantral follicle growth, oocyte maturation, and subsequent embryo development.</p>