N-methyladenosine (mA) is the most common internal modification in eukaryotic mRNA. It is dynamically installed and removed， and acts as a new layer of mRNA metabolism， regulating biological processes including stem cell pluripotency， cell differentiation， and energy homeostasis. mA is recognized by selective binding proteins; YTHDF1 and YTHDF3 work in concert to affect the translation of mA-containing mRNAs， YTHDF2 expedites mRNA decay， and YTHDC1 affects the nuclear processing of its targets. The biological function of YTHDC2， the final member of the YTH protein family， remains unknown. We report that YTHDC2 selectively binds mA at its consensus motif. YTHDC2 enhances the translation efficiency of its targets and also decreases their mRNA abundance. Ythdc2 knockout mice are infertile; males have significantly smaller testes and females have significantly smaller ovaries compared to those of littermates. The germ cells of Ythdc2 knockout mice do not develop past the zygotene stage and accordingly， Ythdc2 is upregulated in the testes as meiosis begins. Thus， YTHDC2 is an mA-binding protein that plays critical roles during spermatogenesis.