Chylous mesenteric cyst is a very rare case, with some vague clinical findings, and it is hard to establish the diagnosis before surgery. The most common complaints post-surgery are abdominal pain and abdominal distention. We report a case of chylous mesenteric cyst in a 4-year-old boy with chief complaint of a lump in the abdomen. Preoperative abdominal ultrasound study could not identify the origin of the mass, and suspected it as a tuberculous peritonitis. A repeat ultrasound examination revealed a multicystic mass, suspected as lymphangioma. From the exploratory laparotomy, we noted a giant mesenterial cyst (20cm in diameter) containing chylous fluid within the ileal mesentery situated 30cm from the ileocaecal junction and made an effect of diminution of the bowel lumen above it, resection and end to end anastomoses was done. Histopathology examination confirmed it as a giant mesenteric cystic lymphangioma.