Myelodysplastic syndromes are refered to as a group of diseases characterized by abnormal clonal proliferation of hematopoietic stem cells with pancytopenia and dysplasia. Recently, it has been documented that ringed sideroblasts are not only confined to the refractory anemia with ring sideroblast (RARS) subtype of MDS, but also contribute to numerous underlying MDS pathophysiological processes as a significant feature of dysplasia. This clonal heterogeneity suggested a pathogenetic role of mitochondrial DNA mutation. Many studies have shown that mitochondrial respiratory chain defects resulting from mutation of mitochondrial DNA may lead to multiple pathophysiologic changes, and may impact on the pathogeneses of MDS.