The aim of this study was to investigate the effect of body mass index on physical activity (PA) level in children between 10-11 years of age. This research is an experimental study. While the universe of the research is composed of children studying in primary schools in Ankara province in 2017-2018 education and academic year, the sample is composed of students studying and teaching in Gazi Primary School in Yenimahalle district. The study included 271 students between the ages of 10 and 11 who voluntarily participated. The necessary permissions were obtained from school principals and student parents before the investigation. This research were taken weight (kg), height (m), PA level (pedometer) and BMI (kg/height[superscript 2]) measurements. SPSS 23 package program was used in the analysis of the obtained data. The mean age of children was 10,57±0,49, mean height was 1,42±8,45 and body weight was 38,33±10,91. BMI was 17.64±3.07 in 10 age group and 19.43±3.94 in 11 age group. The level of PA was determined as 12288±1687 for 10 years and 11328±1721 for 11 years. There was a significant difference between the two groups (p<0.001). There was found to be negatively correlation with PA (r=-0,269) p<0.001, whereas a significant correlation was found between BMI level (r=0,240) p<0,001. A significant correlation was found between BMI and PA level (r-0.817) p<0.001. As a result, it can be said that the body mass indexes of children between 10-11 years of age are in good level and their PA levels are generally active.