Abstract: Objective　To establish the mathematical model of transcutaneous bilirubin (TcB) and total serum bilirubin (TSB) after phototherapy in neonates. Methods　Neonates with pathological jaundice were enrolled from October 2013 to June 2014. The neonates were divided into three groups by gestational age: full-term neonates (gestation age of 37-42 weeks), late preterm neonates (gestation age of 34-36+6 weeks), early and mid-preterm neonates (gestation age of 28-33+6 weeks). The neonates received single or double sided phototherapy. During the phototherapy, the forehead and chest were covered by opaque material. The TcB was measured at forehead, mid sternum, perineum area three times each before and after phototherapy. Meanwhile the TSB was tested. Results　 Two hundred and sixty-one neonates with hyperbilirubinemia were enrolled, among whom there were 169 full-term neonates, 63 late preterm neonates and 29 early and mid-preterm neonates. Before phototherapy, there were significantly correlation of TSB with TcB on forehead, mid sternum and perineum (r=0.813, 0.827, 0.754; P<0.001) and the best correlation was with TcB on mid sternum. The linear regression equation was TSB=1.35TcB-5.50. After phototherapy, there were significantly correlateion of TSB with TcB on forehead, mid sternum, and perineum (r=0.751, 0.807, 0.683; P<0.001) and the best correlation was with TcB on mid sternum. The linear regression equation was TSB=1.01×TcB-0.62. Among three groups, the full-term neonates had the best correlation. Conclusions　After phototherapy, the TcB measured on mid sternum which was covered by opaque material is well correlated with TSB. The linear regression model can be established.