Abstract: s: Objective To analyze the relationship between 1, 25- dihydroxyvitamin D3 level and T cell subsets in patients with gastric cancer. Methods Eighty gastric cancer patients and 80 healthy controls underwent health screenings in our hospital from January 2015 to December 2017 were selected as the subjects of this study. The level of 1, 25- dihydroxyvitamin D3 in peripheral blood was detected by enzyme linked immunosorbent assay and T cell subgroup was detected by flow cytometry. Results There was no significant difference in gender and age between two groups (P＞ 0.05). The level of 1, 25-dihydroxyvitamin D3 in the peripheral blood of gastric cancer group was significantly lower than that of the control group (26.34±4.22)μg/L vs (37.25±5.10)μg/L, P=0.000. The levels of PD-1⁺ and CD4⁺ T cells in gastric cancer group were significantly higher than those in the control group(56.83±4.12 vs 62.31±3.89, 24.12±5.44 vs 33.54±4.12, P ＜ 0.05, respectively), whereas CD8+ and CD4⁺/CD8⁺ levels were significantly lower (26.31±5.19 vs 23.31±4.28, 0.82±0.24 vs 1.31±0.32; P ＜ 0.05, respectively). The blood 1, 25-dihydroxyvitamin D3 was positively corelated with levels of PD-1⁺, CD4⁺ T cell subsets and CD4⁺/CD8⁺ in gastric cancer group(r=0.716, r=0.679, r=0.537; P＜ 0.05, respectively), and negatively correlated with levels of CD8⁺ and CD4⁺/CD8⁺ (r=-0.624, P＜ 0.05, respectively). Conclusion The level of 1, 25-dihydroxyvitamin D3 in peripheral blood of gastric cancer patients is higher than that of healthy people. It's positively correlated with PD-1⁺ and CD4⁺ T cell subsets and CD4⁺/CD8⁺, and negatively correlated with CD8⁺.