The present study tested the mediating role of problematic TikTok use in the relationship between academic stress and academic procrastination, as well as any gender differences. A total of 590 Chinese university students, aged between 17 and 24 years, completed questionnaires measuring their levels of academic stress and academic procrastination at Time 1 (T1), reported on problematic TikTok use at Time 2 (T2) six months later, and academic procrastination at Time 3 (T3) another six months later, while also providing demographic information. The results revealed significant positive associations between T1 academic stress, T1 academic procrastination, T2 problematic TikTok use, and T3 academic procrastination. Moreover, after controlling for age, urban-rural background, family income, TikTok use time, and T1 academic procrastination, T2 problematic TikTok use was found to mediate the longitudinal relationship between T1 academic stress and T3 academic procrastination. Furthermore, gender played a significant moderating role, with the mediating effect being observed only among male university students. The present study is one of the first to explore how problematic TikTok use and gender contribute to the longitudinal effects of academic stress on academic procrastination. The results offer valuable insights into strategies for preventing and managing problematic TikTok use and academic procrastination among university students.