Objective: To investigate the mediating role of peripheral blood T-lymphocyte subsets in Helicobacter pylori (Hp) infection-induced refractory peptic ulcer. Methods: A total of 96 patients with peptic ulcer were enrolled and divided into a non-refractory ulcer group (n=65) and a refractory ulcer group (n=31), with another 30 healthy individuals serving as the control group. The differences in general information and serum T-cell subsets among three groups of patients, specifically T cells (CD3?), helper T cells (CD4?), suppressor T cells (CD8?), CD4?/CD8? ratio, B cells (CD19?), and natural killer cells (CD56?) were explored. Furthermore, the patients with refractory peptic ulcers were classified into the Hp-negative group (n=6) and the Hp-positive group (n=25) according to the Hp test results. The differences in serum T lymphocyte subsets between these two groups were investigated. The mediating role of peripheral blood T-lymphocyte subsets in the relationship between Hp infection and refractory peptic ulcer was examined. Results: Compared with the control group, both the non-refractory and refractory ulcer groups presented decreased serum levels of CD4?, CD4?/CD8? ratio and CD56?, along with elevated CD19? levels. In the refractory ulcer group, CD4? and CD56? levels were further lower than those in the non-refractory group, whereas no significant differences were observed in CD4?/CD8? ratio and CD19? between the two ulcer groups. The refractory ulcer group had markedly lower CD3? levels than both the control group and the non-refractory ulcer group. In terms of CD8? level, it was higher in the non-refractory ulcer group but decreased in the refractory ulcer group when compared with the control group. Compared with Hp-negative patients, Hp-positive patients had elevated serum levels of CD4?, CD8? and CD19? but reduced CD56? levels. Mediation analysis revealed that after adjusting for sex, smoking status and alcohol consumption history, H. pylori infection exerted effects on refractory peptic ulcer by modulating CD3?, CD4? and CD8? levels. Conclusion: Hp infection influences the development of refractory peptic ulcer by modulating peripheral blood T-lymphocyte subsets (CD3?, CD4? and CD8?).