Objective:To investigate the expression levels and clinical significance of serum microRNA (miR) -155 and miR-135b-5p in patients with peptic ulcer complicated with Helicobacter pylori ( Hp) infection. Methods:A prospective study was conducted, and 263 patients with peptic ulcer were selected consecutively from July 2021 to February 2023 at the Affiliated Hospital of Jining Medical College. Among them, 146 cases were confirmed as Hp infection ( Hp infection group) and 117 cases were not complicated with Hp infection (non Hp infection group) by 14C breath test; type Ⅰ Hp infection was in 110 cases, and type Ⅱ Hp infection was in 36 cases by immunoblotting method. The serum expression levels of miR-155 and miR-135b-5p were detected by real-time fluorescence quantitative polymerase chain reaction, serum gastrin level was detected by radioimmunoassay method, and the serum pepsinogen (PG) Ⅰ and PG Ⅱ were detected by enzyme linked immunosorbent assay. The clinical data were recorded. Multivariate Logistic regression analysis was used to analyze the independent risk factors of Hp infection in patients with peptic ulcer; receiver operating characteristic (ROC) curve was used to analyze the efficacy of serum miR-155 and miR-135b-5p in diagnosis the Hp infection in patients with peptic ulcer. Results:The gastrin, PG Ⅰ, PG Ⅱ, ulcer bleeding rate and recurrence rate in Hp infection group were significantly higher than those in non Hp infection group: (108.47 ± 15.35) ng/L vs. (79.63 ± 10.58) ng/L, (295.41 ± 37.26) pg/L vs. (236.75 ± 29.17) pg/L, (44.08 ± 8.52) pg/L vs. (39.29 ± 6.74) pg/L, 25.34% (37/146) vs. 15.38% (18/117) and 21.92% (32/146) vs. 11.97% (14/117), and there were statistical differences ( P<0.01 or <0.05). The serum miR-155 and miR-135b-5p in Hp infection group were significantly higher than those in non Hp infection group (1.94 ± 0.63 vs. 0.95 ± 0.29 and 1.86 ± 0.57 vs. 1.03 ± 0.31), and there were statistical differences ( P<0.01). The serum miR-155 and miR-135b-5p in patients with typeⅠ Hp infection were significantly higher than those in patients with type Ⅱ Hp infection (2.05 ± 0.66 vs. 1.60 ± 0.54 and 1.97 ± 0.61 vs. 1.52 ± 0.45), and there were statistical differences ( P<0.01). Multivariate Logistic regression analysis result showed that serum miR-155, miR-135b-5p, gastrin and PG Ⅰwere independent risk factors of Hp infection in patients with peptic ulcer ( OR = 1.443, 1.436, 1.452 and 1.438; 95% CI 1.165 to 1.787, 1.146 to 1.799, 1.187 to 1.777 and 1.150 to 1.798; P<0.01). ROC curve analysis result showed that the area under the curve of serum miR-155 combined with miR-135b-5p in the diagnosis of Hp infection in patients with peptic ulcer was significantly greater than that of serum miR-155 and miR-135b-5p alone (0.907 vs. 0.839 and 0.836, Z = 2.57 and 2.81, P = 0.010 and 0.005). Conclusions:The serum levels of miR-155 and miR-135b-5p are high in patients with peptic ulcer complicated with Hp infection, and the combination of the two has high diagnostic value for Hp infection in patients with peptic ulcer.