Leiomyosarcoma is a malignant tumor arising from the smooth muscle of any soft tissue. Occurrence of this tumor in the skeletal muscles is rare. A 6-year-old Larry hen was examined because of lameness in one leg. A firm mass was palpable in its right thigh muscle, and radiographs showed extensive involvement of the surrounding soft tissues. The chicken was euthanatized. At postmortem examination, the primary tumor in the thigh skeletal muscles was firm and pink on its cut surface, and metastatic nodules were observed in the liver, spleen, kidneys, heart, and lungs. On histopathologic examination, the primary mass consisted of elongated spindle cells with eosinophilic cytoplasm and blunt-end nuclei arranged as interwoven bundles. Malignancy of the tumor was determined by the presence of pleomorphism, bizarre cells, and high numbers of mitotic figures. Immunohistochemical staining was positive for vimentin, desmin, and α-smooth muscle actin but negative for myogenin. Leiomyosarcoma was diagnosed based on the histopathologic and immunohistochemical findings. To our knowledge, this is the first report in a fowl of leiomyosarcoma in the skeletal muscle with widespread metastasis to other organs.