Objective To assess the degree to which mothers' prepartum personality traits predict breastfeeding status at 6 months postpartum.Study design This prospective cohort study is part of the Norwegian Mother and Child Cohort Study, conducted at the Norwegian Institute of Public Health. A total of 27,753 mothers completed assessment of negative affectivity (NA) and general self-efficacy (GSE) at gestation weeks 17 and 30 and completed a questionnaire about infant feeding at 6 months postpartum. Feeding status was classified with a cutoff at 6 months in the categories of predominant breastfeeding, mixed breastfeeding, and bottle-feeding.Results After adjusting for maternal smoking, age, education, cesarean section, preterm birth, primiparity, and external daycare. NA increased the odds of mixed breastfeeding (odds ratio [OR], 1.16; 95% confidence interval [CI], 1.03 to 1.32) and bottle feeding (OR., 1.32; 95% CI, 1.14 to 1.53) compared with predominant breastfeeding. GSE decreased the odds of bottle feeding (OR. 0.90. 95% CI, 0.84 to 0.97) but not of mixed breastfeeding (OR, 0.98; 95% CI, 0.92 to 1.04) compared with predominant breastfeeding. The adjusting variables were also predictors of breastfeeding behavior in their own light.Conclusions Our results show that NA and GSE are important antenatal predictors of breastfeeding status at 6 months postpartum.