The present study aimed to explore the effectiveness of two typical intrapersonal strategies (cognitive reappraisal, CR; expressive suppression, ES) on interpersonal emotion regulation (IER), and uncover the physiological synchrony pattern underlying this. A sample of 90 friend dyads (N = 180) was randomly assigned to the CR, the ES, or the control group. In each dyad, the target underwent a negative emotional task (induce sadness by recalling a negative event), and the regulator was assigned to implement the CR strategy, the (...) ES strategy, or no action to down-regulate the targets’ negative emotions. Self-reported results showed that compared to the control group, both CR and ES strategies decreased the targets’ negative emotions, and increased the targets’ positive emotions, indicating a successful IER effect. And the ECG results revealed that relative to the control condition, both CR and ES strategies evoked stronger physiological synchrony (heart rate synchrony and heart rate variation synchrony) during the emotion regulation stage of IER. Overall, these findings demonstrated the similar efficacy of reappraisal and suppression strategies implemented by the regulators to improve the targets’ negative emotions, and suggested that the physiological synchrony might have an important relational meaning during the IER process. (shrink)