White sponge nevus (WSN) is a rare autosomal dominant disorder characterised by rough thickening, fissure formation, and a whitish colour change in the oral mucosa. This disorder predominantly affects the nonkeratinized stratified squamous epithelium of the mucosa. We experienced a familial case of WSN (i.e., a mother and her two daughters) and performed keratin gene analysis and immunohistochemical staining. The results of a mutation analysis revealed the presence of a heterozygous missense mutation 344T to G in KRT13, predicting an amino acid change leucine (L) to arginine (R), in the 1A domain of the KRT13 polypeptide. Immunohistochemically, the loss of keratin 4 expression was found.