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Background and Aim: Gefitinib resistance is an urgent problem to be solved in the treatment of non‐small cell lung cancer (NSCLC). Tanshinone IIA (Tan IIA) is one of the main active components of Salvia miltiorrhiza, which exhibits significant antitumor effects. The aim of this study is to explore the reversal effect of Tan IIA on gefitinib resistance in the epidermal growth factor receptor (EGFR)‐mutant NSCLC and the underlying mechanism. Experimental Procedure: CCK‐8, colony formation assay, and flow cytometry were applied to detect the cytotoxicity, proliferation, and apoptosis, respectively. The changes in lipid profiles were measured by electrospray ionization–mass spectrometry (MS)/MS. Western blot, real‐time q‐PCR, and immunohistochemical were used to detect the protein and the corresponding mRNA levels. The in vivo antitumor effect was validated by the xenograft mouse model. Key Results: Co‐treatment of Tan IIA enhanced the sensitivity of resistant NSCLC cells to gefitinib. Mechanistically, Tan IIA could downregulate the expression of sterol regulatory element binding protein 1 (SREBP1) and its downstream target genes, causing changes in lipid profiles, thereby reversing the gefitinib‐resistance in EGFR‐mutant NSCLC cells in vitro and in vivo. Conclusions and Implications: Tan IIA improved gefitinib sensitivity via SREBP1‐mediated lipogenesis. Tan IIA could be a potential candidate to enhance sensitivity for gefitinib‐resistant NSCLC patients. [ABSTRACT FROM AUTHOR]