An objective of the present invention is to provide effective methods for suppressing rejection in organ transplantation, in particular, pancreatic islet transplantation which is useful in treating diabetes. The present invention demonstrated that antibodies against HMGB-1 suppressed the rejection in pancreatic islet transplantation and promoted the survival of grafted pancreatic islets. Thus, the present invention provides agents that comprise an anti-HMGB-1 antibody for suppressing rejection in organ transplantation.