A 79-year-old woman was presented with a 6-month history of painless proptosis in the left eye. On examination, there was a palpable superotemporal mass displacing the left eye inferomedially. Orbital CT revealed a heterogeneous, lobulated mass occupying the left orbital space with no bone erosion or destruction. MRI showed an extraconal, heterogenous, lobulated orbital mass in the lacrimal gland region of the left eye. The lesion was excised, and the diagnosis of leiomyosarcoma was made by histopathologic examination and immunohistochemistry. Systemic examinations were negative for a primary or a metastatic tumor. There was no evidence of tumor recurrence after 12 months of follow-up. Primary orbital leiomyosarcoma is a rare tumor that mainly occurs in older women and presents with painless proptosis. It should be considered in the differential diagnosis of superotemporal extraconal lesions.