<jats:title>Abstract</jats:title><jats:p>The pathogenesis of declining bone mineral density, a universal feature of ageing, is not fully understood. Somatic mitochondrial DNA (mtDNA) mutations accumulate with age in human tissues and mounting evidence suggests that they may be integral to the ageing process. To explore the potential effects of mtDNA mutations on bone biology, we compared bone microarchitecture and turnover in an ageing series of wild type mice with that of the <jats:italic>PolgA</jats:italic><jats:sup><jats:italic>mut/mut</jats:italic></jats:sup> mitochondrial DNA ‘mutator’ mouse. In vivo analyses showed an age-related loss of bone in both groups of mice; however, it was significantly accelerated in the <jats:italic>PolgA</jats:italic><jats:sup><jats:italic>mut/mut</jats:italic></jats:sup> mice. This accelerated rate of bone loss is associated with significantly reduced bone formation rate, reduced osteoblast population densities, increased osteoclast population densities, and mitochondrial respiratory chain deficiency in osteoblasts and osteoclasts in <jats:italic>PolgA</jats:italic><jats:sup><jats:italic>mut/mut</jats:italic></jats:sup> mice compared with wild-type mice. In vitro assays demonstrated severely impaired mineralised matrix formation and increased osteoclast resorption by <jats:italic>PolgA</jats:italic><jats:sup><jats:italic>mut/mut</jats:italic></jats:sup> cells. Finally, application of an exercise intervention to a subset of <jats:italic>PolgA</jats:italic><jats:sup><jats:italic>mut/mut</jats:italic></jats:sup> mice showed no effect on bone mass or mineralised matrix formation in vitro. Our data demonstrate that mitochondrial dysfunction, a universal feature of human ageing, impairs osteogenesis and is associated with accelerated bone loss.</jats:p>