Abstract: Objective : The aim is to explore the relationship between mtDNA (mitochondrialDNA) and gastric cancer by comparing the difference of mtDNA copy number in gastric cancers andpara-cancerous normal tissues. Methods :HV₁, (Hypervariable reigon) and HVZ of mitochondrial D-loop region from 20 gastric cancers and 20 para-cancerous normal tissues were amplified via PCR,meantimep-actin was served as a quantitative standard marker, followed by Polyacrylamide gel elec-trophoresis (PAGE) and silver staining, which compared the difference of mtDNA copy number betweengastric cancers and normal tissues. Results : There existed significantly quantitative difference in HV₂,HVZ (standardized withp-actin) between gastric cancers and normal tissues (P<0.01). mtDNA copynumber was associated with cAMP-PDE and cGMP-PDE (P<0.05). Conclusion : Gastric carcinogene-sis was closely correlated with decreased mtDNA copy number, which would be a new tumor marker.