UNLABELLED: This study aimed to synthesize evidence from primary studies on the acceptability and effectiveness of mindfulness-based interventions (MBIs) for improving lifestyle behaviors and body mass index (BMI) in children with overweight or obesity. We conducted a meta-analysis or followed the Synthesis Without Meta-analysis (SWiM) guidelines to synthesize study findings. The analysis included both mindfulness-only interventions and comprehensive behavioral interventions incorporating mindfulness components. Participants were overweight or obese children, with a mean age below 18 years. A total of 11 studies were included: 7 randomized controlled trials (RCTs), 1 non-randomized parallel-controlled study, and 3 single-group studies. Retention rates for MBIs ranged from 62 to 100%, and participants generally expressed positive attitudes toward the interventions. Regarding effectiveness, no significant improvement in BMI was observed overall (pooled mean difference 0.12 kg/m CONCLUSION: Mindfulness-based interventions are generally acceptable and show potential for improving lifestyle behaviors. However, their impact on BMI remains inconsistent in children with overweight or obesity. Comprehensive behavioral interventions that combine mindfulness practices with conventional approaches may enhance effectiveness. Given the limited evidence, these findings should be interpreted with caution.PROSPERO registration number: CRD42023411790. WHAT IS KNOWN: • Childhood obesity is a significant public health concern, and conventional interventions have achieved limited success. • Mindfulness-based interventions offer a promising alternative to conventional approaches. A systematic review is urgently needed to evaluate their acceptability and effectiveness in improving lifestyle behaviors and body mass index (BMI) in children with overweight or obesity. WHAT IS NEW: • Mindfulness-based interventions are generally acceptable to children with overweight or obesity. • Mindfulness-based interventions show potential for improving lifestyle behaviors, but their effectiveness in reducing BMI remains inconsistent.