Meiotic recombination enables the reciprocal exchange of genetic material between parental homologous chromosomes, and ensures faithful chromosome segregation during meiosis in sexually reproducing organisms. This process relies on the complex interaction of DNA repair factors and many steps remain poorly understood in mammals. Here we report the identification of MEIOB, a meiosis-specific protein, in a proteomics screen for novel meiotic chromatin-associated proteins in mice. MEIOB contains an OB domain with homology to one of the RPA1 OB folds. MEIOB binds to single-stranded DNA and exhibits 3'-5' exonuclease activity. MEIOB forms a complex with RPA and with SPATA22, and these three proteins co-localize in foci that are associated with meiotic chromosomes. Strikingly, chromatin localization and stability of MEIOB depends on SPATA22 and vice versa. Meiob-null mouse mutants exhibit a failure in meiosis and sterility in both sexes. Our results suggest that MEIOB is required for meiotic recombination and chromosomal synapsis.