Breastfeeding could improve a child's health early on, but its long-term effects on childhood behavioral and emotional development remain inconclusive. We aimed to estimate the associations of feeding practice with childhood behavioral and emotional development. In this population-based birth cohort study, data on feeding patterns for the first 6 mo of life, the duration of breastfeeding, and children's emotional and behavioral outcomes were prospectively collected from 2489 mother-child dyads. Feeding patterns for the first 6 mo included exclusive breastfeeding (EBF) and non-exclusive breastfeeding (non-EBF, including mixed feeding or formula feeding), and the duration of breastfeeding (EBF or mixed feeding) was categorized into ≤6 mo, 7-12 mo, 13-18 mo, and >18 mo. Externalizing problems and internalizing problems were assessed with the Child Behavior Checklist (CBCL) and operationalized according to recommended clinical cutoffs, corresponding to T scores ≥64. Multivariable linear regression and logistic regression were used to evaluate the association of feeding practice with CBCL outcomes. The median (interquartile range) age of children at the outcome measurement was 32.0 (17.0) mo. Compared with non-EBF for the first 6 mo, EBF was associated with a lower T score of internalizing problems [adjusted mean difference (aMD): -1.31; 95% confidence interval (95% CI): -2.53, -0.10], and it was marginally associated with T scores of externalizing problems (aMD: -0.88; 95% CI: -1.92, 0.15). When dichotomized, EBF versus non-EBF was associated with a lower risk of externalizing problems (aOR: 0.54, 95% CI: 0.34, 0.87), and it was marginally associated with internalizing problems (aOR: 0.75, 95% CI: 0.54, 1.06). Regarding the duration of breastfeeding, breastfeeding for 13-18 mo versus ≤6 mo was associated with lower T scores of internalizing problems (aMD: -2.50; 95% CI: -4.43, -0.56) and externalizing problems (aMD: -2.75; 95% CI: -4.40, -1.10), and breastfeeding for >18 mo versus ≤6 mo was associated with lower T scores of externalizing problems (aMD: -1.88; 95% CI: -3.68, -0.08). When dichotomized, breastfeeding for periods of 7-12 mo, 13-18 mo, and >18 mo was associated with lower risks of externalizing problems [aOR (95% CI): 0.96 (0.92, 0.99), 0.94 (0.91, 0.98), 0.96 (0.92, 0.99), respectively]. Exclusive breastfeeding for the first 6 mo and a longer duration of breastfeeding, exclusively or partially, are beneficial for childhood behavioral and emotional development.