Leiomyosarcoma is a relatively uncommon malignant lesion that exhibits smooth muscle differentiation. Occurrence of this tumor in the oral cavity is exceedingly rare, reflecting the paucity of smooth muscle in this region. This article presents a rare case of leiomyosarcoma of the buccal mucosa, which was confirmed by immunohistochemical staining. (J. Oral Sci. 50, 215-218, 2008)