Abstract： Objective:To investigate the developmental behavior of early term infants at 6 months and its difference from that of complete full-term infants.Methods:A healthy maternal and infant birth cohort in maanshan city, established in Maanshan Maternal and Child Health Hospital from June 2015 to June 2016. Birth outcomes were copied from the hospital electronic medical record system after delivery. The Chinese Ages and Stages Questionnaires was used to assess developmental behavior. The chi-square test and multivariate unconditional logistic regression model were used to analyze the differences in the behavioral development of early and full term infants.Results:The birth rate of early term infants was 24.74% (500/2 021). The detection rates of communication, gross motor, fine motor, problem solving and individual-social areas in early term infants were 2.1%, 3.2%, 6.1%, 6.3% and 2.7%, respectively. The detection rate of problem-solving area in early term infants was significantly higher than that in the full-term infants (6.3% vs. 3.7%, χ 2=5.42, P<0.05). After controlling for confounding factors, compared with full-term infants, the risk of problem-solving area in early infants was significantly increased ( OR=1.65, 95%CI:1.01-2.70, P<0.05). Conclusion:The risk of behavioral retardation in Early term infants is significantly higher than that in full-term infants, and long-term follow-up and appropriate early development promotion interventions are needed to improve their quality of life.