The prevalence of obesity among Chinese adolescents is rising rapidly, and theoretically informed, scalable weight management interventions are needed. We developed and evaluated the feasibility and preliminary effects of an mHealth nutrition education and mindful snacking intervention for weight loss and improved dietary practices among Chinese adolescents with overweight. We examined whether including implementation intention formation (using if–then plans) improved outcomes. With user consultation, we created a 3-week mindful eating intervention delivered as 10 videos to user smartphones. Participants (n = 55) were randomly assigned to mindful eating or mindful eating + planning. Forty-six (83.6%) participants (age = 16.35 ± 0.48 years; body mass index [BMI] = 25.79 ± 2.05 kg/m2) completed the intervention. Both groups exhibited significant pre- to post-intervention weight loss (M = 1.42 and 1.79 kg, respectively); decreases in snacking frequencies, emotional eating, external eating, and trait craving; and significant increases in mindful eating and eating self-efficacy. No significant intervention group differences were observed. User experience data (n = 16) indicated acceptability and meaningful behavior change. Findings suggest that a smartphone-delivered mindfulness-based intervention for Chinese adolescents living with overweight is feasible and efficacious.