Scomberomorus guttatus is a popular edible fish of Karachi coast and several parasites have been described from this fish. Here histopathology of stomach of fish infected with a new undescribed trematode of genus Prosorchis is reported which caused severe damage to various organs. The main findings were loss of upright position and architecture of mucosal wall of stomach and hypertrophy. Gastric mucosa was collapsed and necrotic, circular and longitudinal muscle layers were degenerated and separated from each other. Thick wall blood vessels and granulomatous lesions were present. This information is useful for fish parasitologist, teachers, students and research workers in this field of study.