Objective To explore the correlation between the expression of serum microRNA(miR)-1298-5p,miR-625-5p,and miR-155 with the degree of Helicobacter pylori(Hp)infection in elderly gastric cancer patients.Methods From January 2021 to November 2023,120 elderly patients with gastric cancer admitted to the hospital from January 2021 to November 2023 were selected as the gastric cancer group,and 130 non-gas-tric cancer patients who underwent gastroscopy were selected as the control group.The expression levels of miR-1298-5p,miR-625-5p and miR-155 in serum were detected by fluorescence quantitative PCR(qPCR).Car-bon 13 urea breath test was used to detect the positive rate of Hp infection in two groups,and the degree of Hp infection in elderly patients with gastric cancer were evaluated.Receiver operating characteristic(ROC)curve was applied to analyze the diagnostic value of serum miR-1298-5p,miR-625-5p,and miR-155 expression levels for Hp infection in elderly gastric cancer patients.Pearson method was applied to analyze the correlation between serum miR-1298-5p,miR-625-5p,miR-155 expression and positive rate of Hp infection in elderly gas-tric cancer patients.Results Compared with the control group,the expression levels of miR-1298-5p and miR-625-5p in serum of gastric cancer group decreased(P＜0.05),while the positive rate of Hp infection and the expression level of serum miR-155 increased(P＜0.05).The expression levels of serum miR-1298-5p and miR-625-5p in elderly gastric cancer patients with Hp grade Ⅰ,Ⅱ,and Ⅲ infection were lower than those without Hp infection,while the expression level of miR-155 was higher(P＜0.05).Patients with poor differ-entiation,lymph node metastasis,and TNM stage Ⅲ-Ⅳ had lower expressions of serum miR-1298-5p and miR-625-5p(P＜0.05),and higher expression of miR-155(P＜0.05)than those with moderate-high differen-tiation,no lymph node metastasis,and TNM stage Ⅰ-Ⅱ.The expression levels of serum miR-1298-5p and miR-625-5p were negatively correlated with the positive rate of Hp infection in elderly patients with gastric cancer(r=-0.443,-0.386,both P＜0.001),and the expression levels of serum miR-155 were positively correlated with the positive rate of Hp infection(r=0.525,P＜0.001).The area under the curve(AUC)of serum miR-1298-5p,miR-625-5p and miR-155 combined diagnosis of Hp infection in elderly gastric cancer pa-tients was higher than that of single diagnosis(P＜0.05).Conclusion The expression levels of miR-1298-5p and miR-625-5p in serum of elderly gastric cancer patients with Hp infection decrease,while the expression level of miR-155 increases.These three factors are related to the degree of Hp infection and have good diag-nostic value for the occurrence of Hp infection.