Non-syndromic hereditary gingival fibromatosis (HGF) is a rare condition, characterized by a progressive gingival hyperplasia that occurs as an isolated disease. Hitherto, only one insertion (g.126,142-126,143insC) in son-of-sevenless-1 (SOS1) gene has been associated with non-syndromic HGF in a Brazilian family. The aim of the present study was to determine if SOS1 is the causative gene of non-syndromic HGF in the Chinese population. Peripheral blood samples were collected from six affected and seven unaffected individuals from three Chinese families with history of non-syndromic HGF. Genomic DNA was extracted and SOS1 gene exons were sequenced. Neither g.126,142-126,143insC nor any other novel mutation was detected in SOS1 gene. Our results suggest that the SOS1 may not be the gene responsible for HGF in these three Chinese families and, therefore, it is possible that other genes are involved in the manifestation of HGF in these Chinese HGF families.