SUMMARY In recent years, there have been more and more reports about cystadenoma. Cystadenoma can occur in many parts of the body, and cystadenoma in different parts may show different clinical symptoms, however, some patients with cystadenoma have no symptoms. The vast majority of cystadenomas are benign lesions, but a small number of cystadenomas can be malignant. For example, a small number of ovarian cystadenomas and pancreatic cystadenomas may be malignant. This study reported a patient with small intestinal cystadenoma diagnosed by pathology. The patient's physical examination revealed a lesion in the left upper abdomen. He had only abdominal distension and no other discomfort. His laboratory examination results were basically normal, i.e. blood routine, urine routine, stool routine, liver function, kidney function, myocardial enzyme, tumor marker, etc. The patient underwent sectional small intestine resection and the pathological sample was analyzed. The histological findings of the resected intestinal sample were consistent with cystadenoma. Computed tomography scan of the abdomen was performed 4 months after the surgery. No recurrence of the tumor was found. The patient recovered in good condition. By consulting the literature, I found very few reports of small intestinal cystadenoma before, it was very rare. This article described the clinical manifestation, diagnosis and differential diagnosis, treatment and prognosis of a case of small intestinal cystadenoma, it suggested that cystadenoma can occur in the small intestine, other than the ovary, pancreas, liver, lung, thyroid, prostate, seminal vesicle, skin, etc. The cystadenoma in small intestine is easy to be mistaken with other tumors, such as small intestine stromal tumor, small intestine adenocarcinoma, small intestine lipoma, small intestine hemangiomas, etc., and it is difficult to fully confirm through imaging examinations, such as computed tomography and magnetic resonance imaging. Laparotomy and histopathological examination are necessary before definitive diagnosis. This disease can be treated by small bowel resection at the affected region and good prognosis can be achieved.