Abstract: This study aimed to investigate the inhibitory effects of Hua Chan Su (HCS) on non-small cell lung cancer (NSCLC) both in vitro and in vivo, and to elucidate the molecular mechanism by which it induces endoplasmic reticulum (ER) stress. Firstly, using the CCK-8 assay to assess the proliferation of human lung adenocarcinoma A549 cells, it was found that HCS significantly inhibited cell proliferation and reduced migratory capacity. Transcriptome sequencing revealed that HCS down-regulated anti-apoptotic genes such as B-cell lymphoma-2 (Bcl2) and was enriched in signaling pathways related to the cell cycle, apoptosis, and ER stress. Further studies demonstrated that HCS enhanced mitochondrial oxidative stress, increased the expression of Bcl2 associated X, decreased the expression of Bcl2, and induced apoptosis. Western blot analysis showed that HCS significantly activated the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-eukaryotic initiation factor 2α (eIF2α)- activating transcription factor 4 (ATF4) signaling pathway in vitro. Combined with a PERK inhibitor, it was confirmed that HCS could trigger apoptosis through the ER stress pathway. In animal experiments, oral administration of HCS (2 and 4 g·kg^-1) for 14 consecutive days significantly inhibited the growth of NSCLC xenografts, with no observed toxicity in major organs. TUNEL staining and Western blot analysis further confirmed that HCS induced tumor cell apoptosis in vivo (all animal experiments were approved by the Institutional Animal Ethics Committee of Nanjing University of Chinese Medicine, approval number: ACU240307). Serum biochemical results suggested that HCS improved liver function and oxidative stress status. In addition, immunohistochemical analysis showed that HCS down-regulated mesenchymal markers such as vimentin, α-smooth muscle actin (α-SMA), and fibroblast activation protein 1 (FAP1), while up-regulating E-cadherin levels, significantly inhibiting the epithelial mesenchymal transition (EMT) process in NSCLC cells. In conclusion, HCS can activate the PERK-eIF2α-ATF4 signaling pathway to induce tumor cell apoptosis and inhibit EMT, indicating its potential application value in the treatment of non-small cell lung cancer.