The steep rise of smartphone use has raised public concerns about smartphone addiction and its associated negative health consequences, such as poor sleep quality; however, limited research has examined the psychological mechanisms underlying these associations. The current study tested the effects of smartphone addiction on poor sleep quality, through self-regulation and bedtime procrastination, among 427 Chinese undergraduate students, aged 18 or older (M = 19.36; female = 66%), who voluntarily completed an anonymous online questionnaire. The results showed that 1/3 of participants reported poor subjective sleep quality. Smartphone addiction and bedtime procrastination had a significant positive relationship, whereas self-regulation had a significant negative association, with poor sleep quality (which was assessed by sleep latency, sleep duration, and subjective sleep quality). Despite its nonsignificant direct effects, the indirect effects of smartphone addiction, via both self-regulation and bedtime procrastination, on the three indicators of poor sleep quality were statistically significant. The findings have supported the premise that both bedtime procrastination and poor self-regulation are risk-enhancing mediators on the association between smartphone addiction on poor sleep quality. Therefore, they should be considered in intervention programs (e.g., self-regulation skill training) to reduce smartphone addiction and improve sleep quality and physical wellbeing among university students.