Left ovarian vein thrombosis is a very rare and infrequent thrombotic condition that mainly occurs in the postpartum or postoperative period. We report a case of a 25-year-old para-1 woman who presented with 2 weeks of postpartum fever and dull aching abdominal pain more on the left side. Before operation, the diagnosis was left adnexal mass secondary to questionable ovarian cyst torsion and she underwent laparotomy. Her intraoperative findings revealed a firm left broad ligament mass with extension to retroperitoneum and it was difficult to demarcate the proximal end. Moreover, on the second day of postoperation, abdominal Doppler ultrasound indicated enlargement of the left ovarian vein that was filled with thrombi having hypoechoic and intermediate echogenicity. After the confirmation of left ovarian vein thrombosis, the case was treated with anticoagulants and broad-spectrum antibiotics and then well improved. Our case climaxes an instant diagnosis and therapeutic significance concerning ovarian vein thrombosis to early manage/avert complications. Besides, the ovarian vein thrombosis diagnosis requires a high index of suspicion for a case presented with fever and abdominal pain.