Objective:To investigate whether ERβ gene expression and polymorphisms can modify the risk of gastric cancer. Methods:Total 100 cases of primary gastric cancer were enrolled as the test group,and 90 cases of gastric ulcer as the control group. Immunohistochemical SP method was used to detect ERβ protein,RT-PCR method to detect the polymorphisms of CA repeat sequence and G1082A in ERβ gene. Results:Positive expression rates of ERβ were 68.0% and 23.3% respectively in the test group and the control group,which had significant differences between two groups (P < 0.01). The positive ERβ expression rates of the subjects with low differentiation degree,high invasion depth,lymph node metastasis and five years death were higher than those with high differentiation degree,shallow invasion depth,without lymph node metastasis and five years survival. And the positive expression rate of ERβ in clinical stages ofⅠand Ⅱ were significantly lower than that in stage Ⅲ (P < 0.01,P < 0.05 respectively). ERβ expression had nothing to do with onset recurrence,age,tumor size,and histological types (P > 0.05). Genotype distribution accords with the Hardy-Weinberg (H-W) genetic balance in CA repeat sequence of ERβ of gastric cancer group and control group(P > 0.05);There was no siginifican difference in comparative genotype distribution of SS,SL,LL and allele frequency of S and L(P > 0.05). In G1082A polymorphism of ERβ,analysis result of RsaⅠand AluⅠdigestion showed that two groups were accord with the H-W genetic balance(P > 0.05);There was no significant difference in comparative genotype of rr,Rr,RR and genotype frequency of r,R/a,A(P > 0.05);but genotype frequency of aa in the test group was higher than that in the control group (P < 0.05). Genotype in G1082A polymorphism of ERβ was closely related to clinical stages,differentiation degree,infiltration depth,metastases situation and the five-year survival condition(P < 0.05),and it wasn’t related to onset recurrence,age,tumor size and histological types(P > 0.05). Only frequency of a/A was closely related to differentiation degree and infiltration depth of gastric cancer(P < 0.01). Conclusion:ERβ polymorphism has close correlation with clinical stages,differentiation degree,infiltration depth,metastases situation and the five-year survival condition in gastric cancer,and genotypes of aa,alleles of a/A in ERβ are critical factors in gastric cancer.