Oxidative stress and generation of reactive oxygen species are strongly implicated in a number of neuronal and neuromuscular disorders, including epilepsy. The functions of selenium as an antioxidant trace element are believed to be carried out by selenoproteins that possess antioxidant activities and the ability to promote neuronal cell survival. Because of this protective role of selenium against oxidative damage, a case-control study was designed to compare its serum level between intractable epileptic patients and normal subjects. Eighty patients who met the criteria of intractable epilepsy were compared with a normal control group of the same age, socioeconomic level, and place of living. Serum selenium level was measured with an atomic absorption spectrophotometer. The mean (± S.D.) of serum selenium were 68.88 (±17.58) ng/mL and 85.93 (±13.93) ng/mL in the patient and control groups respectively. Independent sample t test with P < 0.05 indicated a significant lower mean of serum selenium in the patient group compared with that of the normal control group. However, there was no association between serum selenium and some suggested predictive factors of intractable seizures, including age at the onset of seizures, neonatal seizure, neurologic impairment, and etiology of epilepsy. Measurement of serum selenium in patients with intractable epilepsy should be considered.