In order to further identify expressing difference of cDNA fragments isolated from cDNA representational difference analysis (cDNA RDA) in nasopharyngeal carcinoma(NPC) biopsies and to clone those deregulated genes related with NPC, reverse transcription polymerase chain reaction (RT-PCR) was used to identify the differentially expressing of cDNA fragment, among which AF152605 was found to be down-regulated in sporadic NPC samples (74%). As it were shown by Northern blot, AF152605 is highly expressed in heart,brain, skeletal muscle and placenta whose transcription size is 2.1 kb. Combining bio-informatics, the gene (GenBank accession number AF179285) named as NAG4, was cloned by using library screening, which locates at 6p22～6p23.3. Comparative analysis shows that the NAG4 gene has at least two exons and a “TATAA BOX” sequence lies at upstream of the first exon. And the NAG4 gene encodes a protein proposed of 508 amino acid with predicted molecular mass of 57.4 ku, Blast homology searches reveal that NAG4 protein, containing a bromodomain and several important phosphorylation sites, takes on high similarity to musculus bromodimain-containing protein BP75. Moreover, condon mutation of NAG4 gene was found in HeLa cell line. So it is further demonstrated that NAG4 gene is a good candidate of putative tumor suppressor genes associated with NPC, whose down-expression may be involved in the development of NPC.