Background: Oxidative stress caused by the generation of reactive oxygen species plays an important rolein human carcinogenesis. Manganese superoxide dismutase (MnSOD) Val-9Ala in the mitochondrial targetsequence is the best known polymorphism of this enzyme. The purpose of the current research was to assess theassociation of MnSOD Val-9Ala genotypes with the risk of gastric cancer. Materials and Methods: This casecontrolstudy covered 54 gastric cancer patients compared to 100 cancer free subjects as controls. Extractionof DNA was performed on bioptic samples and genotypes were identified with a polymerase chain reactionrestrictionfragment length polymorphism (PCR-RFLP) method. Results: The frequencies of MnSOD Ala/Ala,Ala/Val and Val/Val genotypes in healthy individuals were 24.3, 66.7 and 9%, respectively. However, in gastriccancer patients, Ala/Ala, Ala/Val and Val/Val were observed in 24.0, 48.0 and 28.0% (p=0.01). In patients thefrequency of MnSOD Val allele was higher (52%) compared to that in controls (42%). Conclusions: The resultsof this study show a positive association between MnSOD Val-9Ala gene polymorphism and risk of gastric cancerdisease in Iranian population.