Background: Chylous mesenteric cyst is a rare entity with variable clinical presentations and possible surgical implications in pediatric age group. Constipation and thick fibrous wall with thin endothelial lining are rarely reported as first clinical presentation and commonest histologic appearance in pediatric patients, respectively. Case presentation: We herein report the case of a 9-year-old male patient presented with an abdominal mass and constipation. Abdominal ultrasonography and computed tomography revealed a well-defined large cystic mass extending to the right abdominal cavity. Laparotomy and histopathology of the excised mass confirmed the diagnosis of chylous mesenteric cyst. Conclusion: To our knowledge, this is the first reported case worldwide as well as in Lebanon with such unusual presentation in pediatric patient. Ultrasonography and CT scan suggest the diagnosis; however, histopathology is often required for confirmation. Complete excision of the cyst yields excellent results.