<p>Personal growth initiative is important for individuals in various life areas. To promote personal development, it is necessary for the current studies to find the protective antecedents of personal growth initiative. This study aimed to examine the effects of physical activity on personal growth initiative as well as the underlying psychological mechanisms. In total, 416 undergraduate and graduate students (231 males and 185 females) participated in the present study. The results suggested that: (1) physical activity was positively associated with personal growth initiative; (2) psychological flexibility and social media addiction separately mediated the relationship between physical activity and personal growth initiative; and (3) psychological flexibility and social media addiction sequentially mediated the relationship between physical activity and personal growth initiative. All the findings could contribute to understanding the relationships and underlying mental mechanisms between physical activity and personal growth initiative, and offer useful evidence for theory development and the selection of intervention methods for personal growth initiative.</p>