Autologous tissue graft is one of the treatment options for a large rotator cuff defect. To develop appropriate strategies for enhanced solid graft integration at the bone-tendon interface and tendon-tendon interface, clarifying the fate of the graft and host cells that contribute to repair and remodeling is necessary. We have developed a new grafting model using green fluorescent protein-transgenic rats and wild-type rats to simulate autologous transplantation for examining the behavior of the host and graft cells in the remodeling process after tendon grafting. We found that the host cells commenced proliferation in the graft at 1 day after grafting. The host cells infiltrated into the graft from the subacromial synovium, proximal tendon, and bone-tendon insertion. The number of graft-derived cells decreased with time. Our result clearly demonstrated that host cells, rather than graft cells, were essential for rotator cuff remodeling after tendon grafting for rotator cuff defect.