JMY is a transcriptional co-factor of p53. Latest work has revealed that JMY is also an actin nucleation factor that regulates new filament assembly and activates Arp2/3 complex in somatic cells; however, roles of JMY in mouse oocyte are unknown. Here we showed the expression and functions of JMY during mouse oocyte meiotic maturation. JMY mRNA is expressed largely from germinal vesicle to metaphase I stage, and gradually decreased during anaphase I, telophase I (TI) and metaphase II (MII) stages. Immunostaining results showed that JMY localized at the spindle and cytoplasm of oocytes. Depletion of JMY by RNAi resulted in symmetric division, failure of spindle migration and cytokinesis during oocyte meiotic maturation, showing a 2-cell-like MII oocyte and TI stage arrest. Actin cap and cortical granules-free domain formation were also disrupted after JMY RNAi, indicating the failure of spindle migration. JMY antibody injection results were consistent with those of JMY RNAi, further confirming the involvement of JMY in oocyte polarity. Our data indicate that JMY is required for spindle migration, asymmetric division and cytokinesis during mouse oocyte maturation.