[Background and aims] Recent experimental data suggest sleep plays a role in brain development. Behavioral and physiologic assessments of neonatal sleep might lead to more developmentally appropriate state regulation for infants in intensive care and assist in daily medical care and predicting the neurodevelopmental outcome. Analysis of sleep patterns using amplitude-integrated electroencephalography (aEEG) might predict further neurobehavioral developmental states in premature infants. The study aimed to evaluate the relationship between sleep states, investigated by aEEG, and short-term neurobehavioral developments in preterm infants.[Study design and subjects] aEEG and neurobehavioral assessments (Neonatal behavioral assessment scale ; NBAS) were performed at 37-39 weeks of post-conceptional age for 10 infants (median gestational age and birth weight were 35 weeks and 2175g. Quiet sleep (QS) data were collected by aEEG over 12 consecutive night hours. QS as the duration of QS intervals and the variation of QS duration periods were analyzed. NBAS were scored by six cluster scores (Habituation, Orientation, Motor, State Range, State Regulation and Autonomic Stability). Correlations analyses examined the relationship between the QS measurement items and NBAS cluster scores.[Results] There were significant negative correlations between the variation of QS duration periods and state range (ρ=-0.71, p<0.05), and the variation of QS duration periods and state regulation scores (ρ=-0.77, p<0.55).[Conclusions] Stable QS periods appear to have some short-term effects on neurobehavioral development in premature infants and therefore protected sleep during premature care is potentially advantageous in improving an infant's neurobehavioral status.