Introduction: Regulatory T cells (Tregs) are important in the tumor microenvironment. Many subpopulations of Tregs have participated in suppressing antitumor immunity. Recently, FOXA1(+) Tregs were reported as a novel subset of Tregs that control autoimmune diseases. However, their clinical value in lung cancer is unknown. Methods: We included 92 subjects in this study. Peripheral blood samples were collected from 15 lung cancer patients. Another 45 advanced stage lung cancer patients with malignant pleural effusion were enrolled for the analysis of FOXA1(+) Tregs in pleural effusions. Lung cancer tissues were collected from 3 patients. In vitro experiments were conducted to ascertain the influence of FOXA1(+) Tregs on T cells. Tumor-bearing mice model was utilized to explore the effects of Foxa1(+) Treg on tumor growth and the prognoses. Results: Our data demonstrated that FOXA1(+) Tregs were increased in lung cancer. Moreover, patients with more FOXA1(+) Tregs showed more liver metastases and poorer treatment responses. In vitro assays revealed that FOXA1(+) Tregs inhibited the proliferation of T cells, the production of IFN-gamma and IL-2 by T cells. FOXA1(+) Tregs promoted tumor growth and indicated poor prognosis in the mice model of lung cancer. Discussion: Collectively, our study is the first to investigate the suppressive function of FOXA1(+) Tregs against T cells in lung cancer, and the results showed that FOXA1(+) Tregs are markers of poor treatment responses in lung cancer patients. The inhibition of FOXA1(+) Tregs represents a promising new strategy to enhance antitumor immunity. (C) 2019 The Authors. Published by Elsevier Inc.