The actigraphic data were examined into the rest-activity rhythms of the mothers and their neonatesfrom the term prepartum(1st - 3rd weeks) to the postpartum (1st -4th weeks, 6th week, 8th week) . The subjectswere five primipara and three multipara and their infants. The actigrams were recorded from the left wrists formothers and from the ankls for infants. Spectral analysis of the actigraphic data by the least squares methoddemonstrated that the circadian spectral peak was observed for four infants in the third postpartum week. In the8th postpartum week, the circadian spectral peak was observed for all infants. Seven mothers showed circadianspectral peak for all terms of experiment. The circadian spectral peaks of one mother (case E) disappeared forthe 1st to 4th postpartum weeks, and reappeared after 6th postpartum week. Three (case A,B,C) in four infantswho showed the circadian spectral peak in early period after birth were stayed in the same room with theirmothers. Three (case F,G,H) in four infants who showed the circadian spectral peaks after 6th postpartum weekwere cared in the separate room from mother's room. In case E, they stayed the same room but the mother'scircadian spectral peak disappeared for the initial 4 weeks postpartum. Therefore the appearance of circadianpeak in the infant' spectra was delayed until 6th week after postpartum when the mother's circadian peakreappeared in her spectra. These results show that the mother's circadian rhythm is the important entrainmentfactor for her infants in the early period of postpartum.