BACKGROUND: Mainland China has the most smartphone users worldwide, especially among college students, while mindfulness intervention can significantly alleviate the level of problematic smartphone use. We examined the effects of a brief mindfulness intervention on problematic smartphone use and investigated if this effect is mediated by self-control. METHODS: Participants were recruited randomly from a university in Beijing of China. Forty-four college students were assigned to a mindfulness group or a control group. The mindfulness group took part in a brief (30 min) single-session mindfulness intervention. The control group was instructed to listen to a neutral news audio recording for the same duration (30 min). The Freiburg Mindfulness Inventory, Mobile Phone Addiction Tendency Scale, and Self-control Scale were used to measure state mindfulness, problematic smartphone use, and self-control of college students at pre-intervention and post-intervention, respectively. RESULTS: Two-way repeated-measures ANOVA revealed that the mindfulness group had significant improvements in state mindfulness (p = .049) and self-control (p = .012), and had significant alleviation in problematic smartphone use (p < .001) at post-intervention. In the regression model, self-control had a mediating effect between mindfulness intervention and problematic smartphone use (95% CI [0.490, 7.216]). CONCLUSIONS: A brief single-session mindfulness intervention can alleviate the level of problematic smartphone use and increase the level of state mindfulness and self-control compared to the control group. Self-control can completely mediate the efficacy of the mindfulness intervention in reducing problematic smartphone use.