The prevalence of postpartum depression is 10-15%, and its symptoms have various consequences for mother and child. One of the psychological features that has recently been examined is negative thoughts after childbirth. According to Wells' metacognitive model of rumination and depression, depressed individuals are focused on negative thinking and believe that their rumination will help them solve problems but cannot control it. It is possible that the evaluation of negative thoughts itself, and not the content of negative thoughts, is related to the level of depression. The cognitive model of depression has not been evaluated yet for this specific period. Therefore, the aim of this study was to determine the role of negative thoughts after childbirth, rumination and metacognition for postpartum depression symptoms. The cross-sectional online study was conducted on a sample of 603 mothers of infants aged between one month and one year. Participants filled out Edinburgh Postnatal Depression Scale (EPDS), Postnatal Negative Thoughts Questionnaire (PNTQ), Ruminative Responses Scale (RRS), Positive Beliefs About Rumination Scale (PBRS) and Negative Beliefs about Rumination Scale (NBRS). The most important cognitive factor in predicting depression symptoms after childbirth was rumination, followed by negative thoughts and negative beliefs about rumination, while positive beliefs about rumination were not a significant predictor. This study provides guidelines for identifying cognitive factors for the onset of depression in mothers of infants and forming tailored cognitive strategies for preventing and reducing negative cognitive factors so that mothers can experience this particular period of life as pleasantly as possible.