Recent studies have suggested some beneficial effects of probiotics on controlling excess weight in adults; such experience is limited in the pediatric age group. This study aimed to assess the anti-obesity and lipid-lowering effects of a synbiotic supplement among children and adolescents. We conducted a randomized triple-masked controlled trial among 70 participants aged 6-18 years with body mass index (BMI) equal or higher than 85th percentile. They were randomly assigned to two groups of equal number to receive synbiotic or placebo for 8 weeks. At the end of the trial, decrease in BMI Z-score, waist circumference, and waist-to-hip ratio were significantly higher in the synbiotic group than in the placebo group. Likewise, synbiotic group had significant decrease in serum triglycerides, total- and low density lipoprotein-cholesterol levels. The beneficial effects of a synbiotic supplement on controlling excess weight and some cardio-metabolic risk factors among children and adolescents can be considered in clinical practice.