〔Abstract〕 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 migra- tion and invasion were assessed through wound healing assays and Transwell assays . Results STAT4 was lowly ex- pressed 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 en- hanced . Conclusion STAT4 is a prognostic marker in LUAD which significantly inhibits the proliferation , inva- sion , and migration abilities of LUAD cells . STAT4 is expected to become a new therapeutic target for LUAD .