Idiopathic sclerosing orbital inflammation (ISOI) is a distinct entity among other orbital diseases. It is characterized by marked fibrosis and inflammatory cell infiltration that can damage orbital structures. Clinical manifestations were variable, including ocular and periocular redness, proptosis, and pain. Ocular motor restrictions and optic nerve dysfunction might occur in severe cases. We herein report a patient of ISOI who presented with total ophthalmoplegia and acute vision loss. His symptoms were relieved mainly as his vision improved to 20/25 after receiving corticosteroid and immunosuppressant therapies. Therefore, ISOI should be one of the deferential diagnoses when we encounter cases with acute orbital apex syndrome. With prompt evaluation and in-time treatment, a favorable outcome is possible.