Introduction: Turner syndrome (TS) is a chromosomal disorder involving the loss of part or all of an X chromosome. General phenotype of TS includes short stature, ovarian failure, webbed neck, coarctation of aorta, and neurocognitive disability. However, it is rarely associated with brain structural abnormalities or comorbid epilepsy. Case: She was born at term without family history. As she grew older, a developmental delay was observed. Magnetic resonance imaging (MRI) of brain and chromosome test were performed, and revealed the findings of TS with 45, XO genotype and hypoplasia of corpus callosum (CC). At 9 months of age, she presented with a first afebrile focal clonic seizure, and was initially treated with carbamazepine. Until she was referred to our hospital at 9 years old of age, she had intractable generalized-tonic-clonic seizure and eyelid myoclonia despite being treated with a lot of antiepileptic drug, profound developmental delay and hypothyroidism. Electroencephalogram found nearly continuous bilateral frontal-dominant diffuse epileptiform discharges, and MRI scan showed calvarial thinkening with diffuse brain atrophy. She was diagnosed with Lennox-Gastaut syndrome (LGS) based on clinical and electroencephalographic findings. Conclusion: Epilepsy in TS is very rare and so far only few cases have been reported, associated with cortical dysplasia. We report a girl of TS showing severe neurodevelopmental impairment, LGS and hypoplasia of CC. The possible dysgenetic role of X-chromosome on dysplastic CC should be discussed.