Cellular and vascularized bone marrow cells have been used to induce donor-specific chimerism in various models of composite tissue allotransplantation. Although thymus transplantation has been reported in the literature, the effect of thymus transplantation on chimerism levels in vascularized bone containing composite tissue allotransplantation has not been reported. In this study, a new method for composite vascularized sternal bone marrow transplant model is descried that can be applied to augment chimerism after transplantation. A total of seven composite osseomusculocutaneous sternum, ribs, thymus, pectoralis muscles, and skin transplantations were performed in two groups. The first group (n = 5) was designed as an allotransplantation group and the second group (n = 2) was designed as an isotransplantation group. Composite osseomusculocutaneous sternum, ribs, thymus, and pectoralis muscles allografts were harvested on thecommon carotid artery and external jugular vein and a heterotopic transplantation was performed to the inguinal region of the recipient rat. Cyclosporine A monotherapy was administered in order to prevent acute and chronic allograft rejection. Animals sacrificed when any sign of rejection occurred. The longest survival was 156 day post-transplant. Assessment of bone marrow cells within sternum bone component and flow cytometry analysis of donor-specific chimerism in the peripheral blood of recipients were evaluated. Our results showed that thiscomposite allograft carried 7.5 × 106 of viable hematopoietic cells within the sternum component. At day 7 post-transplant chimerism was developed in T-cell population and mean level was assessed at 2.65% for RT1n/CD4 and at 1.0% for RT1n/CD8. In this study, a newosseomusculocutaneous sternum, ribs, thymus, pectoralis muscle, and skin allotransplantation model is reported which can be usedto augment hematopoietic activity for chimerism induction after transplantation. © 2012 Wiley Periodicals, Inc. Microsurgery, 2013.