Background. Stomach adenocarcinoma (STAD) is one of the most common malignant tumors. The Janus kinases (JAKs) play a significant part in cellular biological process, inflammation, and immunity. The roles of JAKs in STAD are still not systematically described. Methods. A series of bioinformatics tools were used to clarify the role of JAKs in STAD. Results. JAK3/TYK2 levels were significantly increased in STAD during subgroup analyses based on gender, tumor grade, cancer stages, and nodal metastasis status. STAD patients with high levels of JAK3/TYK2 had poor overall survival, postprogression survival, and first progression. Immune infiltration revealed a significant correlation between JAK3/TYK2 expression and the abundance of immune cells as well as immune biomarker expression in STAD. JAK3/TYK2 was associated with the adaptive immune response, chemokine signaling pathway, and JAK-STAT signaling pathway. Conclusions. JAK3 and TYK2 serve as prognostic biomarkers and are associated with immune infiltration in STAD.