Dioxin and dioxin-like compounds receptor (Ahr) mainly expressed on the surface of regulatory T (Treg) cell and Th17 cell could regulate immunological functions in the Yusho patients. We prospectively analyzed data obtained in a total of 56 cases of Yusho, which include patients identified ('Nintei') or non-identified ('Minintei') or identified as a family member, at the annual health check in 2014. The number of Treg cell showed lower among identified patients compared with non-identified group or family identified group (p = 0.4184 and p= 0.291, respectively). There was also a strong correlation between serum levels of neutral fat and the number of Treg cells (p=0.0313). These results suggest that Treg cell plays a principal role in the immune response among Yusho patients.