Ohtahara syndrome (OS) is known as an intractable epileptic syndrome in neonatal and early infantile period, differentiated from early myoclonic encephalopathy (EME) in its etiology. We report a patient with OS associated with mitochondrial respiratory chain complex (MRC) I defect. With ketogenic diet and mitochondrial cocktail therapy, seizures were completely controlled and suppression-burst patterns disappeared 3 months after starting treatment. It is suggested that OS could be caused by specific metabolic disorder such as MRC defect and the intensive therapies including ketogenic diet, vitamin and coenzyme therapy and antioxidant treatment might be helpful for some patients.