Hesperetin (HST), a natural flavonoid, has potent antitumor effects on lung adenocarcinoma; however, its effects on lung squamous cell carcinoma (LUSC) are currently unknown. The present study aimed to investigate the anticancer effects of HST on LUSC cells. The influence of 37.5, 75 and 150 µM HST on the H1703 cell line, and of 75, 150 and 300 µM HST on the H226 cell line was determined using the Cell Counting Kit‑8 method, cell cycle assay, JC‑1 mitochondrial membrane potential assay and Annexin V‑FITC/PI staining. DMSO‑treated cells were used as the control group. Western blotting was performed to detect the protein expression levels of cyclin B1, CDK1, Bcl‑2, Bax, caspase‑3, cleaved caspase‑3, phosphorylated‑eIF2α, eIF2α, glucose‑regulated protein 78, CHOP, Notch1 and Hes‑1. The relationship between endoplasmic reticulum stress (ERS), Notch1 signaling and apoptosis was examined using the ERS‑inhibitor 4‑phenylbutyric acid (4‑PBA; 500 µM) and the Notch1 signaling activator Jagged‑1 (4 µM). In vivo, mice were divided into control, HST (30, 60 and 90 mg/kg/q2d) and cisplatin (2 mg/kg/q2d) groups to evaluate the anti‑LUSC effects of HST. The results revealed that HST inhibited the viability of H226 and H1703 cells, leading to cell cycle arrest at the G(2)/M phase and the induction of cell apoptosis. In addition, HST downregulated the Notch1 signaling pathway and increased ERS. In H1703 cells, 4‑PBA and Jagged‑1 reduced the expression of apoptosis‑related proteins, and Jagged‑1 also reduced the expression of ERS‑related proteins. In vivo, HST reduced tumor growth without any apparent toxic side effects. In conclusion, HST may exert its antitumor effects by inducing G(2)/M cell cycle arrest and inhibiting the Notch1 signaling pathway to activate ERS‑induced apoptosis, making it a promising agent for treating LUSC.