The goal of primary tendon repair is to increase tensile strength at the time of mobilization. Tendon repair and regeneration using mesenchymal stem cells have been described in several studies; however, the use of adipose derived stem cells (ASCs) for tendon repair has only recently been considered. In order to establish a suitable experimental model for the primary tendon repair using ASCs, this chapter describes the detailed methods for: (1) isolating stem cells from adipose tissue, (2) generation of a primary tendon injury and repair model, (3) evaluating functional restoration by measuring tensile strength, and (4) investigating the mechanisms involved in ASC-mediated tendon healing by histological and immunohistochemical analyses. Topical administration of ASCs to the site of injury accelerates tendon repair, as exhibited by a significant increase in tensile strength, direct differentiation of ASCs toward tenocytes and endothelial cells, and increases in angiogenic growth factors. These findings suggest that ASCs may have a positive effect on primary tendon repair and may be useful for future cell-based therapy.