This study aimed to investigate the effectiveness of electroencephalographic (EEG) biofeedback therapy in reducing anxiety levels and improving overall well-being among patients diagnosed with rectal cancer. A randomised controlled trial was conducted with 150 patients with rectal cancer who were randomly assigned to either the intervention group (n = 75) or the control group (n = 75). The intervention group received 16 sessions of EEG biofeedback therapy over 8 weeks, whereas the control group received standard care. Anxiety levels were assessed using the State-Trait Anxiety Inventory at baseline, post-intervention, 3-month follow-up, 6-month follow-up and 12-month follow-up. Secondary outcomes, including quality of life, sleep quality, treatment adherence, cortisol levels and heart rate variability (HRV), were also evaluated. The intervention group showed significant reductions in state anxiety (p < 0.001) and trait anxiety (p < 0.001) compared with the control group at all post-intervention time points. Significant improvements were also observed in the intervention group for quality of life (p < 0.001), sleep quality (p < 0.001), treatment adherence (p < 0.001), cortisol levels (p < 0.01) and HRV (p < 0.01). The effects were maintained at the 12-month follow-up. Electroencephalographic biofeedback therapy is an effective non-pharmacological intervention for reducing anxiety levels and improving overall well-being in patients with rectal cancer. The findings suggest that incorporating EEG biofeedback therapy into the standard care of patients with rectal cancer may enhance their psychological well-being, quality of life, sleep quality, treatment adherence, physiological stress responses and autonomic function. Long-term benefits were observed, indicating the sustainability of the intervention's effects. Further research is warranted to investigate the underlying mechanisms and potential applications of EEG biofeedback therapy in other cancer populations.© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.