Objective: To discuss the relationship between breastfeeding and the behavioral development of infants and children. Methods: Based on the Ma'anshan Birth Cohort Study, there were 3 474 pregnant women recruited from Ma'anshan Maternal and Child Care Center between May 2013 and September 2014, including 3 273 singleton live births. Follow up the infants to the age of 18 months old. Excluded the infants with incomplete information of breastfeeding and who did not finish the ASQ-3 evaluation in 6 months old and 18 months old, 2 404 valid subjects were included in the study. The information of demographic characteristics, deliver, infants and breastfeeding was collected. The behavioral development were evaluated by the third edition of Ages and Stages Questionnaire (ASQ-3) at 6 months old and 18 months old, and the effect of breastfeeding on behavioral development among infants and children were analyzed by multivariable logistic regression model. Results: The intensity of breastfeeding of infants within 6 months old was (26.56±10.56). The rate of breastfeeding as pure or major intake for infants between 0-5 months old were separately 54.2% (1 303), 54.0% (1 298). 54.0% (1 297), 50.5% (1 213), 34.4% (827) and 9.9% (237). After age, pre-pregnant BMI, intelligence, delivery mode, gender, gestational age, birth weight and family economic status adjusted, compared to never-breastfeeding, continuous breastfeeding for 1-3 months could protect children from severe developmental delay in fine motor domain aged 6 months old (RR=0.36, 95%CI: 0.17-0.79), communication domain aged 18 months old (RR=0.27, 95%CI: 0.08-0.88), and social domain aged 18 months old (RR=0.36, 95%CI: 0.21-0.63). Compared to never-breastfeeding, continuous breastfeeding for more than 4 months could protect children from severe developmental delay in fine motor domain aged 6 months old (RR=0.58, 95%CI: 0.34-0.97), communication domain (RR=0.57, 95%CI: 0.39-0.83) and mild developmental delay (RR=0.65, 95%CI: 0.48-0.87) aged 18 months old and fine motor domain (RR=0.57, 95%CI: 0.39-0.83) aged 18 months old and social domain aged 18 months old (RR=0.57, 95%CI: 0.39-0.83). With the breastfeeding intensity rising, there were less children evaluated as severe development delay in communication domain aged 6 months old, communication, fine motor and problem-solving domains aged 18 months old, with RR (95%CI) at 0.98 (0.96-1.00), 0.96 (0.93-0.99), 0.98 (0.97-1.00) and 0.98 (0.96-1.00); and less children evaluated as mild development delay in communication domain aged 18 months old with RR (95%CI) at 0.99 (0.98-1.00). Conclusion Breastfeeding with longer duration and increased intensity could promote better development in children.