Mutations in rnitochondrial DNA (mtDNA) have been found to be one of the most important causes of sensorineural hearing loss.We report here a clinical, genetic, molecular and biochemical characterization of a Han Chinese pedigree with matemally transmitted nonsyndromic hearing impairment.Seven of nine matrilineal relatives exhibited a variable severity and age-at-onset (8 years old) of hearing loss.Mutational analysis of mtDNA identified the novel homoplasmic tRNASer(UCN) 7505T>C mutation and other 37 variants belonging to haplogroup F1.