Rhabdomyosarcoma, when it occurs in the head and neck, is primarily found in children. Alveolar rhabdomyosarcoma is rarely seen in the oral lesion, comparing to the embryonal and the pleomorphic variants. This is a report of a case of alveolar rhabdomyosarcoma in the mandible in a ten-year old girl who complained of a non-painful swelling on the right cheek. The right lower 1st molar was mobile. Her radiographs revealed an extensive radiolucency with somewhat irregular border on the right mandibular ramus. The right mandibular 1st and 2nd molars lost their lamina dura and were floating. CT images revealed smooth-outlined soft tissue mass occupying the pterygomandibular space, the infratemporal space, and the masseteric muscle with thinning and perforation of the right mandibular angle and ramus. Histopathological and immunohistochemical findings established the final diagnosis of alveolar rhabdomyosarcoma.