Objective To understand the type and frequency of the gene mutation in exon 6 of phenylalanine hydroxylase(PAH) in the children of Ningxia,in order to provide foundation for phenylketonuria(PKU) gene diagnosis and prenatal diagnosis.Methods The exon 6 and flanking introns of 73 cases of classic PKU patients in Ningxia[all confirmed at Ningxia Neonatal Screening Center from Jan.2010 to Jun.2013,and distributed in Ningxia 22 County (city,district),aged from 15 days to 13 years,including 38 male cases,35 female cases,and Hui 39 cases,Han 34 cases] as well as 100 healthy newborn babies(Hui 50 cases;Han 50 cases) were sequentially analyzed by using the approach of PCR direct sequencing.Results There were 6 kinds of mutations detected,including EX6-96A ＞ G(6.85％),Q232X(2.74％),D222G(1.37％),V2301 (1.37％),R176X (0.68％) and N223I (0.68％).Mutation detection rate of exon 6 was 13.70％,and there were 3 mutation types:50.0％ missense mutation (3 types) ;33.3 ％ nonsense mutation (2 types) ;16.7％ cleavage site mutation(1 type).After reviewing the previous studies,the researchers had found out that EX6-96A ＞ G,Q232X and R176X were ever reported in China,and V2301 and D222G had been reported in our country for the first time but N223I was a new kind of PAH gene mutations were not been reported in the world.Conclusions It has defined the gene type and frequency of PAH gene mutations in exon 6 in the children of Ningxia and it will enrich the research of PKU in this area,and provide the basis for the development of gene diagnosis of PKU.