Background. Macrophages are a heterogeneous cell population that plays an important role in the initiation of the inflammatory response to trauma as well as its resolution during healing. However, their role during Achilles tendon healing is unclear. The aim of this study was to investigate if macrophage reduction by using clodronate liposome inject ion would influence the mechanical properties of the healing tendon. Methods. The right Achilles tendon of 46 rats were transected and left to heal spontaneously (day 0). The reduction of macrophages during the inflammatory phase of tendon healing was studied by injecting clodronate liposomes day - 3, - 1 and 1. To study the early remodeling phase, clodronate was injected day 3, 5 and 7. The controls received saline and the rats were evaluated by mechanical testing day 7 and 12, respectively. Results. Clodronate injections during the inflammatory phase increased transverse area (p = 0.006) and stiffness (p = 0.044) day 7. In contrast, no significant effects were seen at day 12. Flow cytometry evaluation confirmed reduction of mature and polarized macrophages. Conclusions. Reduction of macrophages during the inflammatory phase of Achilles tendon healing influenced the mechanical properties, suggesting a regulatory role of macrophages during this phase.