The purpose of this study is to examine maximal oxygen consumption and body composition in children. The subjects of the study consisted 80 girls with mean age of 12.12±0.43 years old and 130 boys with mean age 12.10±0.40 years old. All of the 210 subjects joined the study volunterily. At the end of measurements, the mean values for girls found to be as follows: weight; 48.03±8.73 kg, height; 151.15±5.86 cm, body mass index (BMI); 20.93±04.20 kg/cm2, for boys weight; 43.23±7.10 kg, height; 147.90±8.26 cm, BMI; 19.53±03.43 kg/cm2. Age of children, who joined in study, was smilar characteristic. According to results statistical significant analysis performed; there is no significant differences between of the gender, in the datas, which are body weight, body size and maximal Oxygen consumption (maxVO2) (p>0.05). There is significant differences between of the gender, in the datas, which body weight (p 0.002), BMI (p 0.002) and body fat percent (p 0.002). According to results statistical significant analysis performed; there is significant differences between of gender in data of endomorphy (p<0.05), but there is no significant differences between of gender, in datas in mesomorphy and ectomorphy components (p>0.05). Endomorphy component of girls were higher than boys, because the girls' body fat percentage higher than boys. Although mesomorphy component of boys was higher than girls, there is no significant differences between of gender. Again, it is seen that the boys and girls have similar values of ectomorph components.