Hepatocellular carcinoma (HCC) is a highly aggressive liver cancer with limited therapeutic options, and enhancing radiosensitivity remains a key challenge in improving treatment outcomes. Quercetin (Que) can inhibit the progression of hepatocellular carcinoma (HCC); however, its effect on HCC radiosensitivity remains unclear. This research investigates the role of Que in regulating HCC growth and radiosensitivity, aiming to provide a scientific foundation for enhancing the clinical efficacy of radiation therapy in HCC. The CCK-8 assay was used to determine the optimal treatment conditions for Que and X-rays. Changes in cell growth, cycle arrest, invasion, migration, the relative proportion of JC-1 red and green fluorescence (mitochondrial membrane potential), and the levels of ROS, MDA, SOD, and GSH-Px (oxidative stress) were assessed using flow cytometry, Transwell assays, JC-1 staining, Western blot, and ELISA, respectively, under Que, X-ray, and co-treatment conditions. The effect of miR-216a-3p knockdown on the action of Que was also explored, and the potential pathways by which Que regulates HCC growth and radiosensitivity were investigated in conjunction with in vivo subcutaneous transplantation tumor experiments. The in vitro treatment parameters for Que and X-rays were 100 µM and 4 Gy. Que combined with X-ray therapy enhanced HCC cell radiosensitivity, reduced proliferation, invasion, and migration, and promoted oxidative stress and apoptosis. Que was found to upregulate miR-216a-3p in HCC cells. Rescue experiments with miR-216a-3p knockdowns demonstrated that Que regulates HCC cell radiosensitivity via miR-216a-3p. In vivo research further showed that Que increased tumor sensitivity to X-rays by upregulating miR-216a-3p, thereby inhibiting HCC growth. In conclusion, Que has been shown to enhance HCC radiosensitization by upregulating miR-216a-3p and inhibiting HCC progression. Que may be a promising agent for increasing the radiosensitivity of HCC.