OBJECTIVE: Based on theoretical and empirical evidence, this study examined the longitudinal relationship between problematic smartphone use and bedtime procrastination and the potential mediating role of self-control. METHODS: Between November 2021 and November 2022, a three waves longitudinal design was employed. Wave 1 included 622 Chinese college students (46.95% male, Mage = 18.16, SD = 0.73), with 6-month intervals between waves. The data was collected using self-report assessments. RESULTS: The results of the cross-lagged panel models show that problematic smartphone use positively predicted later bedtime procrastination, and the bedtime procrastination also positively predicted later problematic smartphone use among college students. More importantly, self-control played a mediating role in their bidirectional predictive relationship. CONCLUSIONS: These findings add to the understanding of the causal relationship between problematic smartphone use and bedtime procrastination and reveal the core psychological mechanisms underlying their vicious cycle, with important practical implications for the prevention and intervention of problematic smartphone use and sleep problems.