The purpose of this study was to describe the association between the regularity of sleep patterns for first-time Japanese mothers in the early postpartum period and the sleep and wake activity of their infants and partners. Longitudinal time-series studies of 101 healthy Japanese childbearing couples were conducted between May 2002 and January 2003. Data were obtained from couples at 32–6 weeks pregnancy and 4–5 weeks after birth. The questionnaire packet for each father and mother included a demographic questionnaire, a sleep–wake log for 7 days, a social rhythm metric for 7 days and a morningness–eveningness questionnaire. A four-stage hierarchical multiple regression analysis was performed in which the mother's sleep–wake rhythm strength was the dependent variable. The variance in postpartum sleep–wake rhythm strength for first-time mothers was explained by three predictor variables. Household income, the mother's chronotype during pregnancy and the father's daily social rhythm at 4–5 weeks after birth made unique contributions to the variance (24.7%) in the mother's sleep–wake rhythm strength at 4–5 weeks postpartum. A mother's own tendency to be a morning or evening chronotype and the regularity of the father's daily schedule of activities appear to influence first-time mother's sleep–wake rhythm strength during early postpartum recovery more than disruptions from the infant's sleep–wake activity itself. Health-care providers should counsel couples on how factors associated with the parents themselves may impact on the regularity of a mother's sleep patterns.