Background <p>Understanding postpartum smoking relapse in women is important for protecting both maternal and infant health in the long term. This study aimed to explore the postnatal smoking relapse experiences of women who quit smoking during pregnancy.</p> Methods <p>This descriptive qualitative study was conducted with 11 women who quit smoking during pregnancy and relapsed in the postnatal period. The participants were selected via a purposive sampling method. The study included women who quit smoking during the first trimester of pregnancy and resumed smoking after childbirth; those with a psychiatric diagnosis were excluded. Data were collected through the “Introductory Information Form” and “Semistructured Interview Form” and through online in-depth individual interviews. The interviews were performed between January 1 and 17, 2025. The data were analyzed via a six-stage thematic analysis method.</p> Results <p>The study revealed three main themes: motivations for smoking cessation during pregnancy, factors influencing postpartum smoking relapse, and behavioral processes involved in postpartum relapse.</p> Conclusions <p>Various factors play a role in postpartum smoking relapse, including the intention to resume smoking, low risk perception, breastfeeding, stress, and the attitudes of the social environment. Even if women quit smoking during pregnancy, they should be assessed for the risk of relapse both during pregnancy and in the postpartum period and should be supported when necessary.</p>