During oocyte growth mitochondria undergo a massive biogenesis including an increase in mitochondrial DNA (mtDNA) copy number from approximately 5,000 in primordial oocytes to 200,000 in the fully grown oocyte. Accompanying this increase in mitochondrial biogenesis is an extensive nuclear epigenetic remodelling which establishes the chromatin landscape required for meiotic competence and subsequent embryogenesis. In line with other cell types, recent evidence suggests mitochondria can modulate the oocyte epigenome during oocyte growth (1). Here we have disrupted mtDNA proliferation during oocyte growth and examined effects on oocyte maturation, epigenetic status and the oocyte proteome. To inhibit mtDNA replication during oocyte growth we developed an oocyte-specific mitochondrial DNA polymerase γ (Polg) knockout mouse model by crossing Polgfl/fl female mice (2) with transgenic male mice that carried oocyte-specific growth differentiation factor 9 promoter (Gdf9-Cre). Oocytes from Polg knockout (PolgKO) mice exhibited an approximately eight-fold reduction in mtDNA copy number compared with oocytes from control (Polgcont) mice (32,120 vs. 252,62, P<0.0001). Oocyte maturation was severely impaired in 6 week old PolgKO mice with only 30% of oocytes undergoing germinal vesicle breakdown, compared with 85.1% of control oocytes. Further, the majority of PolgKO oocytes (~64%) are arrested at metaphase I after overnight culture (P<0.0010). Assessment of epigenetic markers revealed PolgKO oocytes had an increased level of nuclear histone 3 lysine 27 trimethylation compared to controls, indicating abnormal epigenetic remodelling. Moreover, single-oocyte proteomic analysis identified altered expression of multiple epigenetic regulators in PolgKO oocytes, supporting the disruption of nuclear epigenetic machinery following mtDNA depletion. In conclusion, we show that inhibition of mtDNA replication during oocyte growth has profound effects on oocyte maturation and leads to alterations in the oocyte epigenome and proteome. We suggest these changes are in part caused by direct mito-nuclear signalling, the mechanism of which remains unknown and requires further investigation.