Mutations in the SCN1A gene, encoding the neuronal voltage-gated sodium channel alpha 1 subunit, cause SMEI, GEFS+, and related epileptic syndromes. We herein report the R1575C-SCN1A mutation identified in a patient with Rasmussen encephalitis. R1575C were constructed in a recombinant human SCN1A and then heterologously expressed in HEK293 cells along with the human beta 1 and beta 2 sodium channel accessory subunits. Whole-cell patch-clamp recording was used to define biophysical properties. The R1575C channels exhibited increased channel availability and an increased persistent sodium current in comparison to the wild-type. These defects of electrophysiological properties can result in neuronal hyperexitability. The seizure susceptibility allele may influence the pathogenesis of Rasmussen encephalitis in this case.