The present inventors assessed the effect of anti-IL-6 receptor antibodies in suppressing chronic rejection reaction. They assessed the effect of anti-mouse IL-6 receptor antibody (MR16-1) administration in suppressing the chronic rejection reaction using a mouse model for post-heart-transplantation chronic rejection. The result of histopathological analysis of transplanted hearts extirpated 60 days after transplantation revealed that fibrosis of myocardium and vascular stenotic lesions, which are pathological conditions characteristic of the chronic rejection reaction, were significantly suppressed in the MR16-1-treated group as compared to the control group. Thus, MR16-1 administration was demonstrated to have the effect of suppressing chronic rejection reaction. Specifically, the present inventors discovered for the first time that the rejection reaction in the chronic phase after organ transplantation was suppressed by administering an anti-IL-6 receptor antibody.