A green moray eel (Gymnothorax funebris) was evaluated for chronic regurgitation. By using flexible endoscopy, the gastrointestinal tract was evaluated and revealed multifocal proliferative gastric masses and an intestinal ulcer. Biopsy specimens revealed gastric mucus gland hyperplasia, intestinal nematodiasis, and mild enteritis. Esophagoscopy and gastroscopy were performed by using a larger endoscope (length, 200 cm). A smaller endoscope (length, 100 cm) facilitated entering the intestinal tract in normograde or retrograde directions. A control eel was also evaluated, and no gross or histologic abnormalities were detected. The case eel was treated with metoclopramide and fenbendazole, responded well to therapy, and regurgitation decreased. A year later, the animal died of unrelated causes. Necropsy revealed coelomic gastric adhesions. The gastric proliferative lesions were associated with degeneration and necrosis of gastric pit mucosa without significant inflammation; etiology was unknown. Gastrointestinal endoscopy proved a useful diagnostic tool for evaluation and biopsy collection in this eel species.