We report a case of fungal melanonychia caused by Trichophyton (T.) rubrum in a 69-year-old female patient. She had brownish to black pigmentation affecting all toe nails that clinically simulated melanonychia. Mycologic examination of toe nails revealed T. rubrum. The causes of melanonychia are numerous, but fungal origin is rare. Although T. rubrum is known to be one of the frequently isolated organisms of fungal melanonychia, there have been no reports of T. rubrum-induced melanonychia yet in Korea.