This study was conducted to determine the influence on sleep rhythm of infants in accordance with their mothers’ sleep behavior. Sleep logs of the 12 mother-baby pairs recorded consecutively from the delivery day to the fourteenth postpartum week were analyzed. Sleep onset (SO) and wake onset (WO) of mothers and their infants showed similar changes at night from the first to the fourteenth postpartum week, but the SO and WO of the mother-baby pairs in primiparae was later than those of mother-baby pairs in multiparae. These results may indicate that the parity of the mothers have modification effects in the development of infants’ sleep rhythm.