Objective To explore the effect in human breast cancer occurring by analyzing the difference of mtDNA copy number in breast cancers and paracancerous tissues. Methods Polymerase chain reaction（PCR）was applied to detect the HV1 and HV2 of mtDNA D-loop in 20 cases invasive ductual breast cancer tissues and 20 cases peritumoral tissues, meantime β-actin was served as a quantitative standard marker, it compared the difference between breast cancer and paracancerous tissues by polyacrylamide gel electrophoresis(PAGE) and analyzing nucleic acid in the Gel-Pro Express system. Results The bands of HV1 and HV2 in breast cancer tissues was weaker than that in peritumoral tissues. There was difference between two groups by HV1 (EM>P/EM><0.05); There was difference between two groups by HV2 (P<0.01). It was detected that the HV1 and HV2 were positively correlated by statistics analyzing (P<0.01). There was no statistic relationship between the difference of mtDNA copy number and age and diameter, but the mtDNA copy number in lymph node metastasis group was higher than that of no lymph node metastasis group, there was difference between two groups (P<0.05). The mtDNA copy number in phase Ⅰof TNM stage was higher than that of phase Ⅱand Ⅲ, and there was difference between phase Ⅱ and phase Ⅲ (EM>P/EM><0.05), there was difference between phase Ⅰ and phase EM>Ⅲ(P/EM><0.05). Conclusion The mtDNA number is descended in i