Objective Amplitude-integrated electroencephalogram (aEEG) is a valuable tool for the continuous evaluation of functional brain maturation in infants.The amplitudes of the upper and lower margins of aEEG are postulated to change with maturation and correlate with postmenstrual age (PMA).This study aimed to establish reliable reference values of aEEG amplitudes, providing quantitative guidelines for assessing aEEG maturation in neonates and young infants.Methods Normal infants (n =274) with PMAs that ranged from 30 to 55 weeks were divided into ten groups according to their PMAs.Two 5-min segments were selected from each aEEG to calculate the upper/lower margin and bandwidths of the tracing automatically.Results Interobserver agreement was achieved with an overall correlation of 0.99.The upper and lower margins of aEEG in both active and quiet sleep clearly rose in infants beyond the neonatal period.The bandwidth defined as the graphic distance decreased almost monotonically throughout the PMA range from 30 to 55 weeks.The lower margin of aEEG was positively correlated with PMA, with a larger rank correlation coefficient during quiet sleep (r =0.89) than during active sleep (r =0.49).Conclusion Reference values of aEEG amplitudes were obtained in infants with a wide range of PMA and constitute a basis for the quantitative assessment of aEEG maturation in neonates and young infants.The normative amplitudes of aEEG margins, especially of the lower margin in quiet sleep, are recommended as reference data for the identification of potentially abnormal aEEG.