Abstract: Mindfulness involves awareness of present experience (Brown & Ryan, 2003), and is related to online vigilance (OV; Johannes et al., 2018). OV denotes the preoccupation with the online world and is linked to smartphone addiction (Throuvala et al., 2020). This study investigated the indirect relationship of mindfulness as a predictor of smartphone use via online vigilance. Undergraduate iPhone users (N = 189) completed the CAMS-R and FMI mindfulness measures (Feldman et al., 2006; Walach et al., 2006), the Online Vigilance Scale (Reinecke et al., 2018), and estimated the proportion of total leisure screen time spent on a smartphone over other devices. Smartphone use was assessed via the Screen Time setting on iPhones. Greater mindfulness indirectly (via OV) predicted lower overall smartphone use, social use, and estimated leisure smartphone screen time. Results suggest that mindfulness training may help to reduce excessive smartphone use by reducing mental preoccupation with the online world.