The aim of this study was to determine the relation between physical activity and functional capacity at the primary school pupils. Many people are not aware that the health of the most important in human life and associated with the movement. In recent decades, the number of obese people, children and adolescents is is significantly increasing. The modern life style of children and young people are increasingly missing movement and outdoor games, is prevalent sedentary lifestyle (TV, Internet, Play Station ..) adverse effects the development of abilities and skills of children and their health status. The study included 80 students of the third grade of primary school, of which 43 boys (mean age 9.30 ± 0.46 years) and 37 girls (mean age 9.29 ± 0.47 years). The students attended two elementary schools in the city of Petrinja., First Primary School and Elementary School Dragutin Tadijanović. The survey was conducted in the school year 2014/2015. The sample of variables consisted of anthropometric measures of body height, weight, skin fold of the upper arm, back skinfold, abdominal skinfold. The functional abilities were measured test run for 3 minutes - F3, which is used to assess the level of functional ability in primary education in the Republic of Croatia. The level of physical activity was estimated PAQ-C questionnaire.   From the results it is evident that of the total sample 60% of them have a normal percentage of body fat, while almost 40% of students with excessive fat in the body. The conclusion of this study indicates a high percentage of students who are overweight. Functional capacity was inversely associated with indicators of obesity, which means that students with high levels of functional capacity have a lower percentage of body fat. School age is the best time to stimulate and positive impact on the growth and development of children and the missed possibilities to that age cannot be recovered in later stages of life.  Keywords: aerobic capacity, functional ability, obesity, students, school