A 3-year-old boy developed left-sided convergent strabismus one week after upper respiratory infection. All examinations, including analysis of cerebrospinal fluid, a tensilon test, and brain MRI, were negative. He was diagnosed with idiopathic sixth nerve palsy. His symptom resolved gradually with vitamin B12, and remitted completely three months after onset. At the age of 6 years, he experienced recurrence of left-sided sixth nerve palsy. After vitamin B12 failed, his symptom responded markedly to intravenous steroid pulse therapy starting on day 26 after relapse. He has been symptom-free for three years since the second remission. Steroid therapy might be effective, and should be considered in children with idiopathic sixth nerve palsy who do not show spontaneous remission.