There are cases in which the presence of a foreign body (FB) is difficult to diagnose based on history taking or clinical examination. We report a case of subconjunctival FB confused with uveal prolapse. A 68-year-old man, who had the history of pterygium excision in his right eye, complained of irritation and congestion in that same eye. He also had the history of growing vegetables in a plastic greenhouse. It seemed to be a suspected uveal mass bulging through a focal scleral thinning site. On the basis of slit-lamp magnification, the lesion was presumed to be a hard and black keratinized mass embedded under the conjunctiva. Histopathologically, the removed mass was revealed to be a seed of the dicotyledones. Patients who show signs of prolapsed uvea or scleral thinning, possibility of a subconjunctival FB should be considered as differential diagnosis. In addition, a removed unknown FB should be examined histopathologically.