Purpose: This study aimed to develop a structural model to explain breastfeeding behavior of primipara based on information-motivation-behavioral skills. Variables were breastfeeding knowledge, breastfeeding motivation, breastfeeding self-efficacy, and parenting stress. Methods: Participants were first-time mothers who were breastfeeding infants from birth to 6 months. Data were collected from 5 pediatric hospitals and 1 public health center in Jeollanam-do from December 24, 2018 to February 28, 2019. A total of 285 questionnaires were included in the analysis. Data were analyzed using IBM SPSS Statistics ver. 20.0 and AMOS 20.0 programs. Results: Fitness statistics for the hypothetical model were appropriate (χ2=48.30 [degrees of freedom= 14, p<0.001], goodness of fit index=0.96, normed fit index=0.89, comparative fit index=0.92, standardized root mean square residual=0.06). Breastfeeding self-efficacy had the most direct and total impact on breastfeeding behaviors (β=0.38, p=0.01). Breastfeeding self-efficacy was directly and totally influenced by breastfeeding knowledge (β=-0.18, p=0.01), breastfeeding motivation (β=0.26, p=0.01). Parenting stress showed a direct effect on breastfeeding self-efficacy (β=-0.14, p=0.02) and breastfeeding behavior (β=0.20, p=0.01), confirming its modulating effect on both variables. Conclusion: Since breastfeeding self-efficacy was the most important variable for the breastfeeding behavior in first-time mothers, nursing interventions should be developed to promote breastfeeding selfefficacy including accurate breastfeeding information and enhanced breastfeeding motivation. Strategies that could relieve or adjust parenting stress should be considered since parenting stress had a causal relationship with breastfeeding self-efficacy and breastfeeding behavior.