Limited evidence suggests that the dietary inclusion of oligofructose, an inulin-type fructan with prebiotic properties, may increase satiety and, thus, reduce energy intake and body weight in overweight and obese adults. The aim of the present study was to assess the effect of oligofructose supplementation for 12 weeks on the BMI of overweight and obese children. A total of ninety-seven children aged 7–18 years who were overweight and obese (BMI >85th percentile) were randomly assigned to receive placebo (maltodextrin) or oligofructose (both at an age-dependent dose: 8 g/d for children aged 7–11 years and 15 g/d for children aged 12–18 years) for 12 weeks. Before the intervention, all children received dietetic advice and they were encouraged to engage in physical activity. The primary outcome measure was the BMI-for-age z-score difference between the groups at the end of the intervention. Data from seventy-nine (81 %) children were available for analysis. At 12 weeks, the BMI-for-age z-score difference did not differ between the experimental (n 40) and control (n 39) groups (mean difference 0·002, 95 % CI − 0·11, 0·1). There were also no significant differences between the groups with regard to any of the secondary outcomes, such as the mean BMI-for-age z-score, percentage of body weight reduction and the difference in total body fat. Adverse effects were similar in both groups. In conclusion, oligofructose supplementation for 12 weeks has no effect on body weight in overweight and obese children.