OBJECTIVES: Childhood obesity is a serious health problem favouring the early development of insulin resistance, type-2 diabetes mellitus and cardiovascular diseases. Our aim was to investigate multidisciplinary weight-control program applying exercise training at maximal fat oxidation (FATmax) zone and diet in three different duration on body composition and physical fitness of overweight children. METHODS: Thirty overweight pupils (BMI > percentile 90%) of three different elementary schools  (age: 11.7+/-1.9) was included. Body composition was determined by bioelectric impedance method. Graded exercise test (Jaeger Oxycon Pro) was used to determine whole-body peak fat oxidation by indirect calorimeter. Training heart rate interval was determined by as +/-10% of FATmax. Physical exercises were prescribed by the physiotherapist. Exercise training was performed 2 times /week in the school using heart rate monitor under the control of the games master. The training periods were 56, 101 and 146 days.  Dietary proposal was given for the parents of children by the dietetics. RESULTS: At the end of the weight-control program percentage of fat mass decreased (35.7+/-4.5 vs. 33.0+/-5.5%; p<0.001), muscle mass increased (22.8+/-4.6 vs. 24.4+/-5.2 kg; p<0.001). VO2max increased at the longest training period only (1841+/- 620 vs. 2011+/-642 ml; p=0.043). CONCLUSIONS: Moderate intensity exercise training and diet resulted in favourable changes in the body composition in a short term whereas the significant improvement of VO2max was started only after 5 months training period.