Body movements during sleep were examined in eight non-eventful preterm babies and two full-term babies using the polygraphic methods including superficial EMG. Typical movements in quiet sleep were startle (St) or generalized phasic movement (GPM) and increased tonic activity in chin muscles. In active sleep, instead of total simultaneous patterns observed in quiet sleep, more un-coordinated and localized movements such as generalized movement (GM), localized tonic movement (LTM), localized phasic movement (LPM) and clonic movement (CM) occurred. Longitudinal study of movements revealed a decrease of St or GPM, GM and LPM. LTM did not decrease with increasing conceptional age. The differences of decreasing tendency among these movements may indicate the differences of maturational changes in the different part of CNS.