Leiomyoma is a rare intraocular tumor that arises from uveal smooth muscle. Herein, we report a large leiomyoma that occupied nearly 50% of the globe, closely resembling melanoma. A 40-year-old female presented with a 17 × 15 × 11 mm amelanotic ciliochoroidal mass causing visual defect in her right eye (OD). Based on transillumination features of tumor shadow and ultrasonographic features of acoustically solid mass, there was low clinical suspicion for leiomyoma or schwannoma, and a preliminary diagnosis of ciliochoroidal melanoma was rendered. Following enucleation, histopathology revealed a paucicellular tumor comprised of spindle cells, with positive immunostaining for smooth muscle actin and negative stains for melanoma markers (S-100 protein, HMB45, and MITF-2). These features were consistent with ciliochoroidal leiomyoma. Benign uveal leiomyoma can achieve an unusually large size and block light transmission on transillumination, features that simulate malignant melanoma.