BACKGROUND: Poor social integration increases risk for poor health. The psychobiological pathways underlying this effect are not well-understood. PURPOSE: This study utilized a migration stress model to prospectively investigate the impact of social integration on change in high-frequency heart rate variability (HF-HRV), a marker of autonomic functioning. METHODS: Sixty new international students were recruited shortly after their arrival in the host country and assessed 2 and 5 months later. At each assessment period, participants provided information on social integration and loneliness and had their resting HF-HRV evaluated. RESULTS: There was an overall decrease in HF-HRV over time. The magnitude of the within-person and between-person effects of social integration on HRV increased over time, such that greater social integration was associated with higher HF-HRV at later follow-ups. CONCLUSIONS: These results suggest that altered autonomic functioning might represent a key pathway linking social integration to health outcomes.