Objective This paper aims to assess the interaction between common variations in catalase (CAT)polymorphic gene and environmental factors for antioxidant defense enzyme in modulating individual susceptibility to colorectal cancer (CRC).Methods A case-control study with 880 colorectal cancer cases and 848 controls was conducted to investigate whether variations in the catalase (CAT) gene,one of the genes involved in scavenging oxidative stress,influenced susceptibility to CRC.Results The interaction between life style and genotypes as well as with their effects on colorectal cancer was deduced from the present study.Significant difference (P=0.01) was identified in the distribution of CAT genotype between the colorectal cancer cases and the controls.The CRC cases had significantly lower mean activity than the controls (P＜0.01).Correlation analyses revealed statistically significant correlations between CAT activity and CAT genotype (P＜0.01).Conclusion The risk of CRC was associated with smoking,low vegetable consumption,high pork and poultry consumptions,and low or high BMI.This is the first study reporting an association of polymorphism CAT-21A＞T with colorectal cancer.Low CAT activity was associated with an increased risk of CRC; however,no evidence was found to support an association between CAT-21A＞T polymorphism and CRC risk.