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Meiotic recombination 11 (Mre11) is a relatively conserved nuclease in various species. Mre11 plays important roles in meiosis and DNA damage repair in yeast, humans and <i>Arabidopsis</i>, but little research has been done on mitotic DNA replication and repair in rice. Here, it was found that <i>Mre11</i> was an extensively expressed gene among the various tissues and organs of rice, and loss-of-function of <i>Mre11</i> resulted in severe defects of vegetative and reproductive growth, including dwarf plants, abnormally developed male and female gametes, and completely abortive seeds. The decreased number of cells in the apical meristem and the appearance of chromosomal fragments and bridges during the mitotic cell cycle in rice <i>mre11</i> mutant roots revealed an essential role of <i>OsMre11</i>. Further research showed that DNA replication was suppressed, and a large number of DNA strand breaks occurred during the mitotic cell cycle of rice <i>mre11</i> mutants. The expression of <i>OsMre11</i> was up-regulated with the treatment of hydroxyurea and methyl methanesulfonate. Moreover, OsMre11 could form a complex with OsRad50 and OsNbs1, and they might function together in non-homologous end joining and homologous recombination repair pathways. These results indicated that <i>OsMre11</i> plays vital roles in DNA replication and damage repair of the mitotic cell cycle, which ensure the development and fertility of rice by maintaining genome stability.