The patient was a 72-year-old male from Nanyang, Henan Province, with a permanent residence in Shenzhen City, who had a habit of fishing using earthworms as baits. He underwent a gastrectomy for gastric cancer in 2023, and nematodes were found parasitizing the jejunum during a routine electronic gastroscopic follow-up; however, but no typical clinical manifestations of respiratory or digestive system were observed. Routine blood tests showed a white blood cell count of 6.61 × 10⁹/L, an eosinophil percentage of 0.7%, and an absolute eosinophil count of 0.05 × 10⁹/L, with all indicators within the normal range. The nematodes were removed using biopsy forceps, appearing red, slender, and atypical in shape with a “Y” configuration, measuring approximately 10 mm in length and capable of autonomous movement. Following staining with Harris’s hematoxylin, the nematodes were identified as male Mammomonogamus under an optical microscope. The patient was diagnosed with Mammomonogamus infection and orally administered with albendazole (400 mg/d, once daily for one week). No Mammomonogamus eggs were detected in the patient’s stool samples one week post-treatment.