Purpose To identify differentially expressed microRNAs (miRNAs) and expression patterns of specific miRNAs during meiosis in human oocytes. Materials and methods To identify differentially expressed miRNAs, GV oocytes and MII oocytes matured at conventional FSH levels (5.5 ng/ml) were analyzed by miRNA microarray. Real-time RT-PCR was used to confirm the changed miRNAs. To validate the dynamic changes of miRNAs from GV to MII stages, oocytes were divided into four groups (#1-4), corresponding to GVoocytes, MI oocytes, MII oocytes matured in conventional FSH level and MII oocytes matured in high FSH level (2,000 ng/ml) respectively. Results Compared with GVoocytes, MII oocytes exhibited up-regulation of 4 miRNAs (hsa-miR-193a-5p, hsa-miR-297, hsa-miR-625 and hsa-miR-602), and down-regulation of 11 miRNAs (hsa-miR-888*, hsa-miR-212, hsa-miR-662, hsa-miR-299-5p, hsa-miR-339-5p, hsa-miR-20a, hsa-miR-486-5p, hsa-miR-141*, hsa-miR-768-5p, hsa-miR-376a and hsa-miR-15a). RT-PCR analysis of hsa-miR-15a and hsamiR-20a expression revealed concordant dynamic changes in oocytes from group 1 to group 4. Conclusion(s) Specific miRNAs in human oocytes had dynamic changes during meiosis. High-concentration FSH in IVM medium led to reverse effect on the expression of hsa-miR-15a and hsa-miR-20a.Keywords miRNA . Oocytes . In vitro maturation . qRT-PCR Oocyte growth and early development requires large amounts of maternally-derived transcripts which are subjected to massive destruction as oocytes mature. Of the estimated 85 pg of polyadenylated mRNAs present in a germinal vesicle (GV)-stage mouse oocyte, 50 pg of mRNAs are degraded during oocyte maturation [1]. Furthermore, transcript degradation is highly selective, primarily affecting genes involved in processes associated with meiotic arrest at the GV-stage and progression of oocyte maturation, such as oxidative phosphorylation, energy production, protein synthesis and metabolism [2]. On the other hand, up-regulation of a number of transcripts during oocyte maturation was also observed in mice, cattle, and humans in recent years [3][4][5].miRNAs are a family of small non-coding RNAs that play important regulatory roles in gene expression. Specifically, miRNA-mediated translational regulation involves cleavage of messenger RNAs or repression of mRNA translation [6]. It has been estimated that 30% or more of human mRNAs are regulated by miRNAs [7]. Likewise, miRNAs may also play an important role in modulating gene expression in oocytes [8].Dynamic changes in miRNA expression during oogenesis were first revealed by a real-time PCR-based miRNA expression profiling method in single mouse oocytes [8]. A Yan-Wen Xu and Bin Wang contributed equally to this study. Capsule Differentially expressed miRNAs in the human oocytes between GV and MII stages were identified by miRNA microarrays. Dynamic changes of miR-15a, hsa-miR-20a, and miR-602 during meiosis were validated by qRT-PCR.