A 10-month-old male infant suffered from progressive abdominal distention and poor appetite for 2-months. Computed tomography revealed a mesenteric teratoma, 15 cm in diameter, extending from the subhepatic area to the pelvic cavity with the small intestine displaced caudally and to the left side of the pelvis. Both the superior mesenteric artery (SMA) and vein were encased within the tumor for the length of at least 5 cm. During operation, tumor was initially dissected through the plane beneath the elevated small bowel mesentery, and the procedure proved rather difficult as the SMA emerged from the tumor, which was accidentally divided. The small bowel turned pale immediately but became pink in color several minutes later. After excision of the tumor, the severed ends of the SMA and SMV were anastomosed smoothly. The color and peristalsis of the small bowel were normal after anastomosis. The patient was discharged on the 5th postoperative day.Mesenteric teratoma is an extremely rare tumor of the germ cells. Complete tumor resection is the main prognostic factor for survival in such cases. Therefore, an important factor for successful surgery is the exact preoperative visualization of the extent of the tumor and meticulous intra-operative assessment of the collateral vasculature. A huge mesenteric teratoma in children, encasing the root of the mesenteric vessels tightly, presents a management challenge to the surgeon. In this particular case, the reversibility of small bowel ischemia caused by accidental severance of the SMA is thought to be due to gradual development of abundant collateral circulation to the small bowel during prolonged compression of the SMA.