A 76-year-old man who had undergone endovascular repair for an infrarenal aortic aneurysm, presented with a late type Ia endoleak 3 years after his operation. Deployment of an aortic cuff did not achieve a better seal at the proximal neck, and the aneurysm developed a rupture. We successfully treated the ruptured aneurysm using transcatheter Onyx embolization only. At 6-month and 1-year follow-ups with contrast-enhanced duplex scanning, no endoleak was seen and sac shrinkage was observed. Onyx is a relatively new liquid embolic agent that is slowly transformed into a solid state by contact with blood. Owing to this unique characteristic, Onyx embolization can be a useful technique for stopping bleeding from an aneurysm in an emergency situation. This is a unique case of the use of an embolization agent in the treatment of aortic aneurysm rupture.