<p>The social adaptation of left-behind children has attracted widespread attention. This study aims to explore the predictive role of the online parent-child communication on the social adaptation of left-behind children, as well as the serial mediation of parent-child relationships and children’s resilience. A total of 539 left-behind children (<i>M</i> = 12.58, <i>SD</i> = 1.74) were surveyed using the Online Parent-Child Communication Scale, Parent-Child Relationship Scale, Resilience Scale, and Social Adaptation Questionnaire. The results indicate that the online parent-child communication positively predicts the social adaptation of left-behind children (<i>P</i> &lt;.05); the parent-child relationship mediates the relationship between the online parent-child communication and the social adaptation of left-behind children; children’s resilience also mediates the relationship between online parent-child communication and social adaptation of left-behind children; furthermore, the serial mediation effect of parent-child relationships and children’s resilience is also established. This study provides a theoretical basis for further research on the social adaptation of left-behind children and for practical interventions aimed at enhancing their social adaptation.</p>