To investigate factors related to resumption of smoking by women after childbirth, the smoking habits of 241 postnatal women, who initially had stopped smoking after pregnancy, in a rural city in Aomori Prefecture, Japan, were studied at 5 -6 days, 1 month, and 12 months after childbirth. At 1 month after childbirth, only nine women had resumed smoking, but a total of 40 women had resumed smoking after 12 months. Factors related to smoking resumption after childbirth included the switching from breast feeding to bottle feeding and the influence of smoking by their spouses. Spousal smoking is an important factor in the resumption of smoking by women after childbirth.