Introduction Mesenteric cysts are rare intra-abdominal lesions of childhood that may vary in presentation from an asymptomatic mass to an acute abdomen. Its incidence range is from 1 per 20,000 to 1 per 250,000 pediatric hospital admissions. And the rarity of these conditions is one of the reasons why the correct preoperative diagnosis is seldom made. In this report, we present a case of mesenteric cyst on proximal ileum in abdominal pain patient. Case 1 A previous healthy 4-year boy was transferred from a primary clinic due to vomiting, abdominal pain and abdominal mass. On physical examination, Bowel sounds were decreased, and 10 cm sized mass was palpable in lower abdomen. Abdominal CT revealed a intra-abdominal cyst measured 12cm, with thin intracystic septations. And abdominal sono showed same result. He was transferred to operation. Intraoperatively, cyst was resected with attached small bowel. Grossly unicystic change intact intestinal serosa with thin cysticwall and measured 4.5 cm, 152g. Imunohistochemical markers were negative and final pathophysiologic result was Lympatic mesenteric cyst. He made a good clinical recovery without complication after operation. Case 2 A 18 month girl was transferred from a primary clinic due to poor oral intake, fever, Periumbilical mass from 2 days ago. On physical examination, Bowel sounds were usual, and Palpable mass was soft, ovoid shape, located in periumbilcal area with direct tenderness. In primary clinic, they tried to do ultrasonography, but they failed scanning the whole mass image because of its huge size. So we conducted Abdominal CT at first. It showed multilobulated cystic mass, sized 12 x 11cm, with multiple enlarged mesenteric lymph node. And our radiologist assumed that it was originated from right ovarian teratoma. But During the Laparotomy, Operator found that the Huge mass was from mesentery. Intraoperatively, cyst was resected, encapsulated proximal jejunum with acute inflammation. Immunohistochemical markers were negative and pathophysiologic result is benign lymphatic cyst. After a few days, She was recovered successfully without complication. Conclusion We report two cases of mesenteric cyst. One is case of 4-year-boy mesenteric cyst with abdominal mass and pain as clinical symptom. The other is case of 18-month-girl mesenteric cyst that misdiagnosed as a ovarian teratoma at first.