Background <p>Ephrin-A4 (EFNA4), a member of the ephrin ligand family, is known to be involved in the progression of various malignant neoplasms. Nonetheless, its specific functional implications in gastric cancer (GC) remain inadequately characterized. Therefore, this study aims to elucidate the underlying mechanisms by which EFNA4 influences GC.</p> Methods and Results <p>Initially, bioinformatics analyses revealed significantly elevated EFNA4 expression levels in gastric cancer tissues when compared with normal counterparts. Additionally, clinical assessments from a cohort of 93 GC patients demonstrated a correlation between EFNA4 expression and factors such as tumor size, AJCC stage, histological grade, and Ki-67 staining score. Furthermore, high levels of EFNA4 expression were associated with decreased overall survival, underscoring its potential as a prognostic biomarker. In vitro functional assays conducted in the human gastric cancer cell line AGS demonstrated that EFNA4 silencing markedly suppressed GC cell proliferation, invasion, and migration. Moreover, knockdown of EFNA4 impeded the process of epithelial-mesenchymal transition (EMT) through the modulation of the PI3K/AKT signaling pathway. Treatment with 740Y-P, a PI3K activator, was observed to enhance the expression of PI3K/AKT-related proteins and reverse the inhibition of malignant behavior in gastric cancer cells caused by EFNA4 knockdown.</p> Conclusions <p>Our findings suggest that EFNA4 may act as an upstream regulator of the PI3K/AKT signaling pathway and could play a role in promoting EMT during the progression of gastric cancer.</p>