Previous studies mainly focused on the role of the epidermal growth factor receptor (EGFR) in tumor cells, whereas the effects of the EGFR on immune responses has not been determined. Our study shows that the EGFR signaling pathway play a role in the regulation of regulatory T cells (Treg cells) in cancer patients. The EGF-like growth factor Amphiregulin (AREG) protein was frequently up-regulated in a tissue microarray, which was associated with worse overall survival. Additionally, in sera, tissue specimens, and effusions of lung or gastric cancer patients, up-regulated AREG protein enhanced the suppressive function of Treg cells. AREG maintained the Treg cell suppressive function via the EGFR/GSK-3β/Foxp3 axis in vitro and in vivo. Furthermore, inhibition of EGFR by the tyrosine kinase inhibitor gefitinib restored the activity of GSK-3β and attenuated Treg cell function. β-TrCP was involved in GSK-3β-mediated Foxp3 degradation, and mass spectrometry identified Lys³⁵⁶ as the ubiquitination site of Foxp3 by β-TrCP. These findings demonstrate the posttranslational regulation of Foxp3 expression by AREG in cancer patients through AREG/EGFR/GSK-3β signaling, which could lead to Foxp3 protein degradation in Treg cells and a potential therapeutic target for cancer treatment.