Neonatal hyperbilirubinemia is more common in Asia.A case-control study was conducted to explore the respective contribution of known gene modifiers to the development of severe hyperbilirubinemia on a group of neonates of southern China.71 term infants with bilirubin level > 20 mg/dL (340 μmol/L) and 65 controls were enrolled in the study.Variation status of hepatic bilirubinconjugating isoenzyme uridinediphosphoglucuronosyltransferase 1 A1 (UGT1A1), glucose-6-phosphate dehydrogenase (G6PD) and thalassemia genes in our study cohort were determined by direct sequencing or genotype assays.Among these case infants, 9 were confirmed with G6PD deficient, 6 heterozygous for α or ββ-thalassemia, and 55 of them had at least one heterozygous UGT1A1 functional variant, including 14 homozygous for UGT1A1 variation.Aside the predominant c.211 G >A (Gly71Arg) variant, four coding variants of UGT 1A 1 gene [c.684C>A (Pro229Gln), c.1091C>T (Pro364Leu), c.1352C>T (pro451leu) and c.1456C>T(Tyr486Asp)] were observed in our case neonates.The results of multivariate logistic regressions, adjusted for covariates, revealed odds ratios (Ors) for neonates who carried heterozygous, homozygous variation at nucleotide 211 of UGT1A1 gene and G6PD deficiency were 3.61(1.36-9.61), 17.13(1.91-153.87) and 17.28(1.69-176.31) compared with those having the wild genotype and normal G6PD activity, respectively.In conclusion, in addition to G6PD deficiency screening, UGT1A1 genetic analysis, expecially the UGT1A1*6(c.211G > A, p.Arg71Gly) polymorphism, may serve as a diagnostic aid for individuals with significant hyperbilirubinemia.UGT1A1*6 polymorphism screening may be taken into consideration for early diagnosis and treatment of severe hyperbilirubinemia newborns in southern China.