BACKGROUND The serum creatinine (SCr) concentration in neonates is generally high for its body size, compared to those of infants. The aim of the present study was to investigate the effect of maternal SCr on neonatal SCr through measurements of prenatal maternal SCr and neonatal SCr from birth to postnatal Day 5. In addition, postnatal changes in SCr were compared between term and preterm infants, given that few studies have addressed this topic. METHODS The retrospective study subjects were 151 neonates whose Scr was measured consecutively from birth to postnatal Day 5 and 124 mothers whose SCr was measured prenatally. RESULTS There were significant correlations between maternal SCr and neonatal SCr at birth (r = 0.858, p < 0.001) and on postnatal Day 1 (r = 0.235, p < 0. 001). The SCr of term infants (median 0.69 mg/dL, range 0.54 - 0.96 mg/ dL) were higher than those of preterm infants (median 0.63 mg/dL, range 0.43 - 1.23 mg/dL, p < 0.001) at birth; however, these values were reversed on postnatal Day 1 (Term: median 0.75 mg/dL, range 0.51 - 1.13 mg/dL, Pre-term: median 0.88 mg/dL, range 0.56 - 1.25 mg/dL, p < 0.001). There were differences in the timing of reaching to peak SCr between preterm and term neonates. In addition, birth weight might affect SCr concentrations after birth. CONCLUSIONS The results of this study suggest that neonatal SCr is influenced by maternal SCr, although the effect disappears by postnatal Day 2. Moreover, glomerular filtration rate differs between term and preterm infants.