Mesenteric vein thrombosis (MVT) is rare in pregnant women, but could be a potentially life-threatening condition. We present here a case of MVT in 32-year-old Korean woman at 8 weeks’ gestation. She conceived via in vitr o fertilization-embryo transfer and was taking oral estrogen for luteal support. She was referred to the emergency unit of our hospital complaining of whole abdominal pain which was aggravated the last 2 days along with vomiting. A clinical examination revealed tenderness on palpation of left lower abdomen and tachycardia. Diagnostic laparoscopy was performed and revealed ileal ischemia in 50cm length. Resection of necrotic portion of ileum and side-to-side anastomosis was performed via open laparotomy. She was treated with low molecular weight heparin postoperatively and delivered by cesarean section at term without additional complications. MVT should be considered in the differential diagnosis of a pregnant woman with an acute abdomen.