Naturalistic developmental behavioral interventions target developmentally appropriate skills in young children with autism spectrum disorders using behavioral techniques in naturalistic interactions. Naturalistic developmental behavioral interventions demonstrate strong empirical support and frequently utilize caregiver training of intervention strategies. However, our understanding of the mechanisms of change linked to naturalistic developmental behavioral interventions remains limited. Based on retrospective, secondary data analyses from three previously conducted randomized controlled trials of caregiver-mediated naturalistic developmental behavioral interventions, this study examined the direct effect of intervention on caregiver naturalistic developmental behavioral intervention strategy use and how caregiver changes mediate intervention effects on children's social communication. A total of 419 videos from 229 dyads consisting of autistic children (M = 32.5 months/ages 1-5 years) and caregivers were included in analyses using the masked ratings of the measure of naturalistic developmental behavioral intervention strategy implementation-caregiver changes (MONSI-CC) and brief observation of social communication change (BOSCC-SC). Using longitudinal mediation analyses, we examined the mediation effect of caregiver behavioral changes on children's outcomes. Results demonstrated a significant intervention effect on changes of caregiver naturalistic developmental behavioral intervention strategy use (MONSI-CC) and of changes of caregiver strategy use (MONSI-CC) on child social communication change (BOSCC-SC) scores, but no overall total effect of intervention on changes of child social communication (BOSCC-SC). This study demonstrates the mediating role of caregiver behavior on the child intervention response, a first step toward better understanding underlying mechanisms in naturalistic developmental behavioral interventions.