The present invention relates to a cell therapy composition for preventing or treating immune disease comprising mesenchymal stem cells and immunoregulatory T-cells as an active ingredient. By infusing mesenchymal stem cells and immunoregulatory T-cells, which are the cellular therapeutic agent of the present invention, into bone marrow transplant animals, rejection to the host is suppressed after the engraftment of the transplanted bone-marrow to thus obtain the effect of reducing graft-versus-host disease and immune disease. Moreover, the effect of such GVHD reduction is much greater than the one obtained when only mesenchymal stem cells are infused. Accordingly, the cell therapy composition of the present invention having the above-mentioned effects can be useful in the prevention or treatment of immune disease.