Objective To investigate the expression characteristics of granzyme B （GZMB） and C-X-C motif chemokine ligand 9 （CXCL9） in gastric cancer （GC） tissues， explore their association with the tumor immune microenvironment （TME）， and evaluate their clinical prognostic significance. Methods Bioinformatic analyses were conducted using public databases （TIMER， GEPIA， UALCAN） to validate the expression levels of GZMB and CXCL9 across various cancer types， with a focus on GC. Paired tumor and adjacent normal tissue samples were collected from 89 GC patients who underwent radical gastrectomy at Nanyang First People's Hospital between 2018 and 2019. The mRNA expression levels of GZMB and CXCL9 were measured using quantitative real-time PCR （qRT-PCR）， and their associations with clinicopathological characteristics were statistically analyzed. Immune cell infiltration levels were estimated using the TIMER and GSCA databases. Diagnostic performance was evaluated through receiver operating characteristic （ROC） curve analysis， while survival outcomes were assessed using data from the Kaplan-Meier Plotter database and patient follow-up records. Results Both database analysis and qRT-PCR results demonstrated that GZMB and CXCL9 expression levels were significantly elevated in GC tissues compared to adjacent non-tumor tissues （P < 0.05）. Clinical correlation analysis revealed no significant associations between mRNA expression levels of GZMB and CXCL9 and clinicopathological parameters， including gender， age， pathological type， tumor differentiation， TNM stage， tumor size， or lymph node metastasis （P > 0.05）. Immune infiltration analysis indicated that both genes were significantly positively correlated with CD8⁺ T cell and dendritic cell infiltration （P < 0.05）， while showing a negative correlation with B cell infiltration （P < 0.05）. ROC curve analysis showed that the combined detection of GZMB and CXCL9 yielded an AUC of 0.890 （95%CI： 0.843 ~ 0.936）， which was higher than that of GZMB alone （AUC = 0.832， 95%CI： 0.772 ~ 0.891） or CXCL9 alone （AUC = 0.782， 95%CI： 0.715 ~ 0.850）. Survival analysis further revealed that patients with high expression of GZMB and CXCL9 had significantly improved overall survival compared to those with low expression （P < 0.05）. Conclusion GZMB and CXCL9 are highly expressed in GC and are strongly associated with the infiltration of anti-tumor immune cells. These molecules represent promising diagnostic biomarkers for GC， and their elevated expression is correlated with a more favorable prognosis in patients.