Double-stranded DNA (dsDNA) derived from pathogen- or host-damaged cells triggers innate immune responses when exposed to cytoplasm. However, the machinery underlying the primary recognition of intracellular dsDNA is obscure. Here we show that the DNA damage sensor, meiotic recombination 11 homolog A (MRE11), serves as a cytosolic sensor for dsDNA. Cells with a mutation of MRE11 gene derived from a patient with ataxia-telangiectasia-like disorder, and cells in which Mre11 was knocked down, had defects in dsDNA-induced type I IFN production. MRE11 physically interacted with dsDNA in the cytoplasm and was required for activation of stimulator of IFN genes (STING) and IRF3. RAD50, a binding protein to MRE11, was also required for dsDNA responses, whereas NBS1, another binding protein to MRE11, was dispensable. Collectively, our results suggest that the MRE11-RAD50 complex plays important roles in recognition of dsDNA and initiation of STING-dependent signaling, in addition to its role in DNA-damage responses.