The present invention relates to a composition containing PIAS3 as an active ingredient for the prevention or treatment of cancer or immune disease. More specifically, the present invention relates to a composition containing the PIAS3 gene or an expressing protein thereof as an active ingredient for the prevention or treatment of cancer or immune disease, to an immunosuppressant composition, to a method for reducing or inhibiting undifferentiated T cells into Th17 cells using the PIAS3 gene or an expressing protein thereof, and to a method for activating regulatory T cells.
