Abstract: Bilirubin metabolism plays an important role for the human，free bilirubin can pass through cell membranes， blood-brain barrier and lipid membranes freely， resulting in cell toxicity and neonatal kernicterus.Fetal bilirubin metabolism is different from the adults′. Because of the immaturity of fetal liver function， only a small amount of fetal bilirubin can be transformed into non-toxic conjugated bilirubin via fetal liver， while most of the unconjugated bilirubin dissolved in the plasma in the form of bilirubin-albumin complex is transferred to mother to be metabolized by bilirubin carriers in the placenta. In certain pathological conditions， such as high concentration of bilirubin or low concentration of albumin， bilirubin-albumin complex may be dissociated from albumin binding sites to free bilirubin， which can result in neurotoxic effects on fetus，causing fetal adverse outcomes.

Key words: Bilirubin, Kernicterus, Hyperbilirubinemia, Fetus, Placenta