Aim: To investigate the influence of smoking on postpartum depression. Methods: One thousand fifty-one women, in a rural city in Aomori Prefecture, Japan, prospectively fulfilled the selection criteria and completed self-reporting questionnaires on postnatal depression at 5-6 days, 1 month, 4 months, 7 months and 12 months after childbirth, using the Edinburgh Postnatal Depression Scale (EPDS) and a life and social events scales including smoking habits. Results: Seven hundred seventy-seven women were non-smokers. Among two hundred seventy-four women who were smokers before becoming pregnant (26% of pregnant women), 241 women quit smoking during pregnancy and 33 women continued smoking. Smoking habits were significantly associated with sociopsychological states and we found that EPDS scores of smokers were significantly higher than EPDS of non-smokers. The EPDS scores of both non-smokers and smokers were higher at 5-6 days, but were stable from 1 month to 12 months, after childbirth. Fifty-one women who quit smoking after childbirth resumed smoking during he 1-12 month periods after childbirth. The EPDS scores of 51 women who resumed smoking were significantly reduced after they resumed smoking. Conclusion: The EPDS scores of smokers were higher than those of non-smokers and a smoking habit may help to alleviate postpartum depression.