Abstract: Objective: To investigate the effects of combination use of DST and CTLA4Ig to the prolongation of skin allograft survival in mouse and to study the mechanism of CTLA4Ig to prolong the survival of allograft. Methods: Skin allograft recipient mice were treated with CTLA4Ig or DST alone or in combination.Survival time of skin allografts was observed and mixed lymphocyte reaction (MLR) was examined to detect the reactivity of spleen cells of recipient mice to cells from donor mice or third party. Results: Survival time of skin allografts was prolonged in group treated with both DST and CTLA4Ig with the reactivity of spleen cells of recipient mice to cells of donor mice degraded specifically while groups treated with DST or CTLA4Ig alone show no difference to negative control group. Conclusions: Combination use of DST and CTLA4Ig can prolong the survival time of skin allograft in mice.The presence of passenger leukocyte in organ allograft may be helpful to the allograft tolerance inducing effect of CTLA4Ig.