Fuzheng Kang-Ai (FZKA) decoction is mainly composed of 12 components with different types of herbs. In the last decade, FZKA has been used as an adjuvant treatment for lung cancer in clinical practice. Our previous studies have confirmed that FZKA shows a strong anti-cancer activity, significantly increases the clinical efficacy of gefitinib and reverses gefitinib resistance in non-small cell lung cancer (NSCLC). However, the molecular mechanism still needs to be further elucidated.The aim of this study was to investigate the role and mechanism by which FZKA inhibited the cell growth, proliferation and invasion of lung adenocarcinoma(LUAD) and reversed the acquired resistance of gefitinib for the therapy in LUAD.Cell viability assay and EDU assay were used for detecting of cell viability and cell proliferation. Transwell assay was performed to measure cell invasion. Western Blot and qRT-PCR were used for protein and gene expression test. The gene promoter activity was determined by dul-luciferase reporter assay. The in situ expression of protein was measured by cell immunofluorescence. Stabilized cell lines were established for stable overexpression of EZH2. Transient transfection assay was used for gene silence and overexpression. Xenograft tumors and bioluminescent imaging were used for in vivo experiments.FZKA significantly inhibited the cell viability, proliferation and cell invasion of LUAD, the combination of FZKA and gefitinib had a great synergy on the above processes. Moreover, FZKA significantly decreased EZH2 mRNA and protein expression, FZKA reversed the resistance of gefitinib by down-regulation of EZH2 protein. ERK1/2 kinase mediated the down-regulation of EZH2 reduced by FZKA. In addition, FZKA decreased the expression of Snail and EGFR by decreasing EZH2. Overexpression of Snail and EGFR significantly reversed the effect of FZKA-inhibited cell invasion and cell proliferation. More important, the combination of FZKA and gefitinib enhanced the inhibitory effect on EZH2, Snail and EGFR proteins. Furthermore, the growth inhibition and reversal of gefitinib resistance induced by FZKA were further validated in vivo. Finally, the expression and clinical correlation of EZH2,EGFR and Snail in cancer patients were further validated using bioinformatics analysis.FZKA significantly suppressed tumor progression and reversed gefitinib resistance by regulating the p-ERK1/2-EZH2-Snail/EGFR signaling pathway in LUAD.Copyright © 2023. Published by Elsevier B.V.