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Restoration of biomechanical strength following surgical reconstruction of tendon or ligament insertion tears is challenging because these injuries typically heal as fibrous scars. The authors hypothesize that injuries at the tendon-bone interface would benefit from reconstruction with decellularized composite tendon-bone grafts.Tendon-bone grafts were harvested from Sprague-Dawley rats. Grafts subjected to decellularization were compared histologically and biomechanically with untreated grafts ex vivo and in a new in vivo model. Wistar rats underwent Sprague-Dawley allograft reconstruction using a pair-matched design. The rats were killed at 2 or 4 weeks. B-cell and macrophage infiltration was determined using immunohistochemistry, and explants were tested biomechanically.Decellularization resulted in a decrease in cells from 164 ± 61 (untreated graft) to 13 ± 7 cells per high-power field cells (p < 0.005) and a corresponding significant decrease in DNA content, and preserved scaffold architecture of the tendon-bone interface. Biomechanical comparison revealed no difference in failure load (p = 0.32), ultimate tensile stress (p = 0.76), or stiffness (p = 0.22) between decellularized grafts and untreated controls. Following in vivo reconstruction with tendon-bone interface grafts, decellularized grafts were stronger than untreated grafts at 2 weeks (p = 0.047) and at 4 weeks (p < 0.005). A persistent increase in B-cell and macrophage infiltration was observed in both the capsule surrounding the tendon-bone interface and the tendon substance in untreated controls.Decellularized tendon-bone grafts display better biomechanical properties at early healing time points and a decreased immune response compared with untreated grafts in vivo.