Background: Intraluminal thrombosis in the aneurysm sac is commonly seen in abdominal aortic aneurysm (AAA). Complete acute thrombosis of an AAA is a rare and catastrophic event. Method: We report a patient with acute AAA thrombosis presenting as bilateral lower limbs critical ischemia. A79-year-old male with a past history of AAA presented with acute onset of bilateral leg pain, coolness, weakness and numbness. His lower extremity pulses including femorals were absent bilaterally on physical examination. Urgent computed tomography angiography showed an infrarenal AAA measuring 45 mm in diameter. The aneurysm sac and bilateral common iliac arteries were completely occluded. Emergency open repair of AAA and bilateral iliac thrombectomy were successfully performed under general anesthesia. Result: Bilateral femoral pulses were present and the neurological deficits were completely resolved after operation. Patient recovered well and was asymptomatic at 3-month follow-up. Conclusion: Acute thrombosis of aortic aneurysm could be an unusual cause of lower limb ischemia, prompt diagnosis followed by surgical revascularization is essential to avoid prolonged ischemia.