We assessed the clinical characteristics and efficacy of neurotransmitters and levetiracetam in a patient with hyperphenylalaninemia due to dihydropteridine reductase (DHPR) deficiency who developed epileptic seizures. A boy with DHPR deficiency, who had been successfully treated with tetrahydrobiopterin (BH4), levodopa, and 5-hydroxytryptophan (5-HTP) since he was 2 months old, started having monthly episodes of blurred vision, loss of consciousness, and falls at the age of 12 years. He was taking BH4 510 mg/day, levodopa 670 mg/day, 5-HTP 670 mg/day, and entacapone 300 mg/day. We evaluated the seizure semiology, EEG findings, and efficacy of levodopa, 5-HTP, and levetiracetam (LEV). His seizures were comprised of an abrupt loss of awareness and eye deviation to the right. Interictal EEG showed slightly slow posterior-dominant rhythm in 7-8 Hz; intermittent, irregular slowing in the bilateral parieto-occipital region; and multiregional independent spikes in bilateral hemispheres. Ictal EEG showed a seizure pattern starting at the left temporal region. Brain MRI showed diffuse signal increase of deep white matter on T2-weighted and FLAIR images. Dosage increase of levodopa to 1340 mg/day, of 5-HTP to 1500 mg/day, or of both did not suppress seizures. Levetiracetam 2000 mg/day markedly reduced seizures without any adverse events. Patients with DHPR deficiency can develop epileptic seizures of partial onset which can be successfully and safely treated with LEV.