Using the experimental system of GFP (Green florescence Protein) bone marrow transplanted rats, we implanted the Vicryl absorbable suture thread in subcutaneous tissue and examined the formation of foreign body granuloma histopathologically. We also compared the main cellular components, namely, the macrophage and foreign body giant cell immunohistochemically using GFP to confirm their origin. Histologically, the disintegrated suture thread was observed as a circular in void surrounded by the proliferation of macrophages and foreign body giant cells. Fibrous connective tissue including the fibroblasts was interposed among large masses. Even after 6 months, some clusters considered to be residues of macrophages that grew on the suture were still remained. Immunohistochemical examination of GFP showed that all proliferated macrophages and foreign body giant cells were GFP-positive. However, the relatively thin fibrous tissues formed on the outermost layer of the granulation tissue growth were mostly GFP-negative. Based on the results of the experiment, the macrophages and foreign body giant cells that are GFP-positive were derived from the mesenchymal tissue of transplanted bone marrow tissues.