The current study examined the influence of perceived social support on social anxiety among Korean returnee cross-cultural individuals (CCIs)—defined as those who lived in two or more cultural environments during the developmental period ranging from birth to 18 years—focusing on the moderated mediation mechanism with re-acculturative stress as a mediator and self-compassion as a moderator. Study participants consisted of 175 Korean undergraduate students (97 females, mean age = 22.6, SD = 1.8). Results indicated that perceived social support decreased social anxiety via re-acculturative stress. However, the indirect effect of perceived social support on social anxiety through re-acculturative stress differed according to the level of returnee CCIs’ self-compassion. Specifically, the mediating effect of re-acculturative stress on Korean returnee CCIs’ relationships between perceived social support and social anxiety was significant only for those with low levels of self-compassion. It was insignificant for those who reported high levels of self-compassion, indicating that self-compassion had a buffering effect. These findings imply that providing returnee CCIs with sufficient social support and helping them reduce re-acculturative stress would decrease their social anxiety, particularly when they are self-compassionate.