The incidence of profound congenital hearing loss is about 1 in 1,000 live birth. There are more than 50 distinct genetic loci (known as DFNB loci) at which mutations can cause recessive hearing loss. DFNB4, one recessive locus for deafness, also maps to 7q31 considerably for nonsyndromic hearing loss and Pendred Syndrome which has been named PDS gene. Pendred syndrome (PS, MIM 274600) with an estimated frequency 1-8 per 100,000, is an autosomal recessive disorder and classically characterized by sensor neural hearing loss and goiter. Here, we reported a family with Pendred syndrome that in which a new mutation, T420I, in the homozygous state caused the condition. Also there was a 9-year-old boy in the related family with hearing loss and with no signs of thyroid dysfunction or goiter, whom was compound heterozygous for PDS mutations including 1197delT and T420I. Both of these mutations result to PDS syndrome. However we are not sure if the 9-year old boy show the goiter appearance in near future, but the results could be used as the prognostic factor. Consequently we should follow up the patient. Besides all, characterization of mutations in PDS gene can guide us to early diagnosis of Pendred syndrome and consequently early treatment of the patients maybe show the clinical features of hypothyroidism in later onset.