Abstract: 　Objective　To explore the characteristics of the phenylalanine hydroxylase (PAH) gene mutations in the patients with phenylalanine hydroxylase deficiency (PAHD) in Jiangsu area, and to analyze the mutational spectrum of PAH and the correlation between genotype and phenotype in patients with PAHD. Methods Totally 70 children with PAHD and their parents were involved in this study. All 13 exons and their flanking intronic sequences of PAH gene were directly sequenced in these patients. Results 125 different mutations were detected with the relative frequency of 89.29% among 140 allelic genes. The prevalent mutations were EX6-96A>G (15.20%)，R243Q (14.40%) and R241C (13.60%). The prevalent mutations in classic phenylketonuria（PKU） were R243Q and EX6-96A>G (42.86%). The prevalent mutations in moderate PKU were EX6-96A>G, R241C and R111X (40.74%). The prevalent mutations in mild PKU were R241C，EX6-96A>G and R243Q (57.89%). The prevalent mutations in mild HPA were R241C and R243Q (40.00%). The consistency between prediction of the biochemical genotype and the observed phenotype was 65.63%, especially in classic PKU (81.25%). Significant correlations were disclosed between pretreatment levels of phenylalanine and AV sum (r=-0.77, P<0.001). Conclusions The frequency distribution of common PAH gene mutation in Jiangsu area was different from the other regions, the genotype of PAHD patients has correlation with the phenotype.