〔Abstract〕 Objective To investigate the expression level of signal transducer and activator of transcription 4(STAT4) in lung adenocarcinoma(LUAD), and to analyze its impact on the proliferation, invasion, and migration abilities of LUAD cells. Methods Gene expression omnibus data base(GEO),human protein atlas(HPA) and Kaplan-Meier Plotter databases were used to explore the expression of STAT4 in LUAD and its effect on the survival of patients with LUAD. Stable LUAD cell lines with STAT4 knockdown were constructed using lentiviral packaging technology, and the knockdown efficiency of STAT4 was assessed via RT-qPCR. The effects of STAT4 on LUAD cell proliferation were evaluated using CCK-8 assays and colony formation assays, while the impacts on cell migration and invasion were assessed through wound healing assays and Transwell assays. Results STAT4 was lowly expressed in LUAD, and its low expression was unfavorable to the survival of LUAD patients. After STAT4 was knocked down in LUAD, the proliferation, invasion and migration abilities of lung adenocarcinoma cells were enhanced. Conclusion STAT4 is a prognostic marker in LUAD which significantly inhibits the proliferation, invasion, and migration abilities of LUAD cells. STAT4 is expected to become a new therapeutic target for LUAD.