The high prevalence of problematic smartphone use (PSU) among adolescents has raised public concern due to its negative health consequences, such as sleep problems. The current longitudinal study aimed to investigate the prospective effects of PSU and fear of missing out (FoMO) on both bedtime procrastination and sleep duration among Chinese adolescents. Three hundred eighteen Chinese high school students (M = 16.92, SD = 0.67) completed an anonymous questionnaire at both baseline and 6-month follow-up. The results of the analyses showed that both PSU and FoMO were correlated with greater bedtime procrastination and shorter sleep duration. However, path analysis revealed that only baseline PSU (β =.11, p <.05) but not baseline FoMO (β =.05, p >.05) predicted bedtime procrastination at the 6-month follow-up, while sleep duration assessed at the follow-up survey was significantly predicted by only baseline bedtime procrastination (β = −.16, p <.01). Our findings support the adverse effect of PSU on adolescent sleep health, while that of FoMO may not be as direct as expected. Future studies with three or more waves of data collection are recommended for properly testing the prospective, probably indirect, effects of PSU, FoMO, and other emotional or cognitive factors on sleep quality.