The present study reports on the first evaluation of a parenting intervention utilizing a smartphone app, BabyMind. The intervention aimed to facilitate mothers' mind-mindedness-attunement to their infants' internal states. Mothers in the intervention group (n = 90) used the BabyMind app from their infants' births and were followed up at age 6 months (n = 66). Mothers in the control group (n = 151) were recruited when their infants were age 6 months and had never used the BabyMind app. Mind-mindedness when interacting with their infants was significantly higher in intervention group mothers than in control group mothers. The intervention was equally effective in facilitating mind-mindedness in young and older mothers. These findings are discussed in terms of the potential for interventions utilizing smartphone apps to improve parenting and children's developmental outcome in vulnerable and hard-to-reach groups.