Objective : To explore the relationship between single nucleotide polymorphisms ( SNPs) in D-loop region of mitochondrial DNA ( mtDNA) and mtDNA copy number and the risk of dermatomyositis ( DM) ，and its in- fluencing factors． Methods : 74 patients with DM and 92 healthy controls were included in the study． Genomic DNA was extracted from peripheral blood and the target fragment of mtDNA D-loop region was amplified by PCR technique，and the products were subsequently sequenced．Serum levels of ROS were assessed using a high-sensi- tivity reactive oxygen species detection kit．The expression levels of cytokines，interleukin ( IL) -5，IL-13，inter- feron-γ ( IFN-γ) ，IL-2，IL-6，IL-10，tumor necrosis factor-α ( TNF-α) and IL-4 were measured using Flow Fluo- rescence Immunmicrobeads Assay．Wilcoxon rank-sum test was used to assess the potential correlation between cy- tokines and SNPs associated with DM risk．The relative copy number of mtDNA was measured using quantitative re- al-time polymerase chain reaction ( qPCR) analysis． Results : Two SNPs ( 16304T / C，16519T / C) were found to be associated with the risk of developing DM，and alleles 16304C ( χ2 = 4. 937，P = 0. 026) and 16519C ( χ2 = 4. 405，P = 0. 036) in the mitochondrial D-loop region were confirmed to be associated with DM development risk． The DM risk-associated allele 16304C was significantly associated with lower IL-4 expression ( P = 0. 016) ．The mtDNA copy number was significantly higher in DM patients than in controls ( P ＜0. 001) ． Conclusion Mitochondrial D-loop SNPs can be potential biomarkers for DM risk，and SNPs may be involved in DM by influencing cytokines．DM shows high expression of mtDNA copy number，and the increase in mtDNA copy number may lead to mitochondrial dysfunction，which triggers the pathogenesis of DM．